Как найти максимальное значение словаря python

Are you wondering how to find the minimum and maximum values in a Python dictionary? Here you will find the answers you are looking for.

The easiest way to find the minimum or maximum values in a Python dictionary is to use the min() or max() built-in functions applied to the list returned by the dictionary values() method. You can also pass just the dictionary to the max() or min() functions but in that case you have to use the optional key argument to identify minimum or maximum based on dictionary values and not on keys.

We will go through multiple ways to solve this problem so you can choose the one you prefer.

Let’s start coding!

How Do You Find the Maximum Value in a Python Dictionary?

Let’s assume that we have created a game and that we are storing the points of all players in a dictionary.

>>> points = {'Jake': 100, 'Andy': 450, 'Kate': 230}

The first thing I can think about to calculate the maximum value in a dictionary would be to use a Python built-in function.

Python provides a built-in function called max() that returns the largest item in an iterable.

Also, one of the methods provided by Python dictionaries is values() that returns a list of all the values in the dictionary.

>>> print(points.values)
<built-in method values of dict object at 0x7f9448181500>

Firstly let’s call the values() method on our dictionary to see what we get back:

>>> print(points.values())
dict_values([100, 450, 230])

Then try to pass this list to the max function…

>>> print(max(points.values()))
450

We got back what we wanted, the maximum value in the dictionary.

In the next section we will see how to get the maximum value in the dictionary while also keep tracked of the key mapped to that value.

Get Maximum Value and Its Key From a Dictionary in Python

In the previous section we have seen that the Python max function can be used with iterables.

Is a Python dictionary an iterable?

A Python dictionary is an iterable because it has the dunder method called __iter__. To verify all the methods that belong to a dictionary you can use the command dir(dict).

>>> dir(dict)
['__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'clear', 'copy', 'fromkeys', 'get', 'items', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']

Here is what happens if you pass the points dictionary defined in the previous section to the max function:

>>> max(points)
'Kate'

The max function returns the key with maximum value in the dictionary. In this case the keys are compared alphabetically.

This is not what we want considering that we want to get the maximum value in the dictionary and not the maximum dictionary key.

To get the maximum value we have to pass the optional argument key to the max function. The argument key is used to specify a one-argument ordering function.

This is the same approach used with the built-in sorted function.

We pass points.get as the key argument so the max function goes through all the keys in the dictionary and gets the maximum after calling the points.get() method for each key (this method returns the value associated to a given key).

>>> max(points, key=points.get)
'Andy'

Once again…

We are passing points.get to the key argument to get the maximum based on the values in the dictionary and not based on the keys.

This time the max function returns the key ‘Andy’ because it’s the key associated to the highest value in the dictionary (450).

To get the actual value we simply have to retrieve the value mapped to the dictionary key obtained with the previous code:

>>> print(points[max(points, key=points.get)])
450

And if we want to print both key and maximum value we can use the following code…

>>> print("Key associated to the maximum value: {} - Maximum value: {}".format(max(points, key=points.get), points[max(points, key=points.get)]))
Key associated to the maximum value: Kate - Maximum value: 450

To print the previous message we have used the string format method.

How Do You Get All the Keys with the Highest Value in a Dictionary?

In the previous examples there was only one maximum value in the dictionary.

But what happens if in the previous dictionary we have the same maximum value associated to different keys?

Here is what I mean…

>>> points = {'Jake': 100, 'Andy': 450, 'Kate': 450}

In this case both Andy and Kate have 450 points and when I use the code created in the previous section, here is the result:

>>> print("Key associated to the maximum value: {} - Maximum value: {}".format(max(points, key=points.get), points[max(points, key=points.get)]))
Key associated to the maximum value: Andy - Maximum value: 450

We only get back the key ‘Andy’ and this is not correct.

How can we get back a dictionary that contains both keys associated to the maximum value? (in this case Andy and Kate).

We can start with the maximum value and then identify the keys whose value matches the maximum value.

To create this new dictionary we will use a dictionary comprehension.

So let’s calculate the maximum value first and store it in the variable max_value:

>>> max_value = max(points.values())

Then use a dictionary comprehension to create the new dictionary by using the keys that match the maximum value.

>>> {key:value for key, value in points.items() if value == max_value}
{'Andy': 450, 'Kate': 450}

To understand the comprehension expression above you have to remember what the dictionary items() method returns.

>>> print(points.items())
dict_items([('Jake', 100), ('Andy', 450), ('Kate', 450)])

Does it makes sense now?

In the dictionary comprehension we go through each tuple in the list and we take key and value from the tuples whose value matches the maximum value.

How to Use the Python Max Function with a Lambda Expression

Let’s go through another way to get the maximum value and the key associated to it from a Python dictionary.

Note: with this approach we are making the assumption that the maximum value in our dictionary can only be one.

Take the following dictionary:

>>> points = {'Jake': 100, 'Andy': 450, 'Kate': 200}

We will calculate the maximum tuple in the list returned by points.items().

>>> print(points.items())
dict_items([('Jake', 100), ('Andy', 450), ('Kate', 200)])

Here is the result we get by simply applying the max built-in function to the list of tuples above…

>>> max(points.items())
('Kate', 200)

Hmmm….this is not what we want…

We are getting this tuple back from the max function because the function is returning the maximum tuple using the first element of the tuple as ordering criteria.

If you want to provide a different ordering criteria to the max() function we can pass the optional key argument that allows to specify a one-argument ordering function.

In this case our ordering function will be a lambda that picks the second element in each tuple to identify the maximum tuple.

The second element in a given tuple represents a value in the original dictionary.

The lambda function we will pass is…

lambda data: data[1]

The call to the max function becomes:

>>> max(points.items(), key = lambda data: data[1])
('Andy', 450)

As you can see we are getting back the correct key / value pair from the dictionary based on the fact that 450 is the maximum value.

Using operator.itemgetter() with Max Function to Get the Maximum Value in a Dictionary

There is also another way to write the lambda function we have seen in the previous section:

lambda data: data[1]

This lambda function can be replaced by the operator.itemgetter() function, part of the operator module.

By passing the index 1 to operator.itemgetter() you get back the second item of each tuple in the points.items() list.

>>> import operator
>>> max(points.items(), key = operator.itemgetter(1))
('Andy', 450)

As you can see the itemgetter function is used as key argument to identify the maximum value in the dictionary.

If you only want to get back the maximum value you can retrieve it by accessing index 1 of the tuple returned.

>>> max(points.items(), key = operator.itemgetter(1))[1]
450

Another Way to Find the Maximum Dictionary Value Using a Lambda and the Max Function

Let’s have a look at another way to find the maximum value in a dictionary by using a lambda function together with the max function.

In the previous section we have used the lambda function to identify the maximum second item in each tuple returned by points.items().

This time we will work on the original dictionary points instead of points.items().

We want to define a lambda function that given a key returns the value mapped to that key. Then we will use this lambda as optional key argument (it will be used as ordering function by the max function).

The lambda function will be:

lambda dict_key: points[dict_key]

Given the following dictionary…

>>> points = {'Jake': 100, 'Andy': 450, 'Kate': 200}

We can use the max function as shown below:

>>> max_value = max(points, key = lambda dict_key: points[dict_key])
>>> print(max_value)
Andy

Note: in the same way we have seen in the previous section this approach doesn’t work if the same maximum value is assigned to multiple keys.

Note 2: the key argument of the max() function has nothing to do with the dictionary key. To make this clear I have used dict_key in the lambda function.

See this as an exercise to practice the use of dictionaries, lambdas and the max function.

How Do You Find the Minimum Value in a Python Dictionary?

To find the minimum value in a Python dictionary you can use the min() built-in function applied to the result of the dictionary values() method.

This is similar to the approach we have used previously to calculate the maximum value.

Let’s use the following dictionary…

>>> points = {'Jake': 100, 'Andy': 450, 'Kate': 450}

And here is the minimum value in the dictionary calculated using the min() function.

>>> min_value = min(points.values())
>>> print(min_value)
100

And now with a dictionary comprehension and an if statement we can create a dictionary that contains all the keys that match the minimum value.

>>> {key:value for key, value in points.items() if value == min_value}
{'Jake': 100}

Let’s confirm it also works if multiple keys are mapped to the minimum value.

>>> points = {'Jake': 100, 'Andy': 450, 'Kate': 450, 'Jeremy': 100}
>>> {key:value for key, value in points.items() if value == min_value}
{'Jake': 100, 'Jeremy': 100}

It works!

Find Maximum Value in a Python Dictionary Using an “Inverse” Dictionary

If you think we have gone through enough ways to retrieve the maximum or minimum value in a dictionary, think twice 🙂

I want to show you an alternative approach that is quite different from the ones we have seen so far.

Start from the following dictionary:

>>> points = {'Jake': 100, 'Andy': 450, 'Kate': 230}

Now…

I want to swap keys and values in the dictionary.

You will see why shortly…

The format of the original dictionary is:

{key1: value1, key2: value2, ..., keyN: valueN}

The new dictionary will be:

{value1: key1, value2: key2, ..., valueN: keyN}

Let’s do this first and then you will see how you can use the new dictionary to get the maximum value.

To swap keys and values in the dictionary we can use a dictionary comprehension.

>>> points_swapped = {value:key for key, value in points.items()}
>>> print(points_swapped)
{100: 'Jake', 450: 'Andy', 230: 'Kate'}

Make sure you understand this comprehension before you continue reading.

Now, we can use the max() function with the new dictionary to get the maximum value in the dictionary.

>>> print(max(points_swapped))
450

The same applies to the min() function that returns the minimum value in the dictionary:

>>> print(min(points_swapped))
100

Conclusion

Wow, we have seen lots of different ways to retrieve maximum and minimum values from a Python dictionary.

It has been a great opportunity to review Python concepts like:

  • Built-in functions (min / max) with and without the optional key argument.
  • Dictionary methods: dict.values() and dict.items().
  • Lambda functions.
  • The itemgetter function of the Python operator module.
  • Dictionary comprehensions.

I hope you have found this article useful.

And now, what else would you like to learn?

Let me know in the comments below 🙂

I’m a Software Engineer and Programming Coach. I want to help you in your journey to become a Super Developer!

In this Python tutorial, we will discuss the Python find max value in a dictionary.

To obtain the maximum value from the dictionary, use the in-built max() function of Python.

Here we will discuss the following 3 methods

  • Using dict.items()
  • Using max() and lambda function
  • Using max() and dict()

In this Python section, we are going to discuss different methods for finding the max value in a dictionary.

Method-1: Using dict.items()

Here we will know how to find the maximum value in a dictionary using the dict.items() method:

# Import the operator module
import operator

# Create a dictionary with some key-value pairs
max_dict = {'Australia':178, 'Germany':213, 'Japan': 867}

# Use the operator.itemgetter() method in combination with the max() function to find the key with the maximum value
new_ma_val = max(max_dict.items(), key=operator.itemgetter(1))[0]

# Print the key with the maximum value
print((new_ma_val))

In the above code, we first import the operator module, which provides functions for working with operator overloading.

  • Then we create a dictionary max_dict with key-value pairs. We use the operator.itemgetter() method in combination with the max() function to find the key with the maximum value.
  • The operator.itemgetter() method is used to extract the value from the tuple by using the index passed to it, which is 1 in this case. The max() function compares the values and returns the key-value pair that has the maximum value.
  • The key is extracted from the returned tuple by using [0] indexing and is assigned to the variable new_ma_val. Finally, we print the key with the maximum value which is “Japan” with 867 as the max value.
Python find max value in a dictionary by using dict
Python find max value in a dictionary by using dict

Method-2: Using max() and lambda function

Here we will know how to find the maximum value in a dictionary using the max() and lambda methods:

# Create a dictionary with some key-value pairs
Country_dict = {'China':982, 'Egypt':758, 'Malaysia' : 12}

# Use the max function with a lambda function to find the key with the maximum value
new_val = max(Country_dict, key= lambda x: Country_dict[x])

# Print the key with the maximum value
print("maximum value from dictionary:",new_val)

In the above code, we first create a dictionary Country_dict with key-value pairs.

  • Then we use the max() function with a lambda function to find the key with the maximum value. The lambda function takes a single argument x which is the key of the dictionary and returns the value associated with the key.
  • The max() function then compares the values and returns the key that has the maximum value. Finally, we print the key with the maximum value, which is ‘China’ with 982 as the max value in this case.
Python find max value in a dictionary by using max with lambda function
Python find max value in a dictionary by using max with a lambda function

Method-3: Using max() and dict()

Here we will know how to find the maximum value in a dictionary using the max() and dict() methods:

# Create a dictionary with some key-value pairs
name_dict = {"Oliva": 18, "potter": 56, "Harry": 15}

# Extract the values from the dictionary and assign it to a variable
new_val = name_dict.values()

# Use the max function to find the maximum value
maximum_val = max(new_val)

# Print the maximum value
print("Maximum value from dict:",maximum_val)

In the above code, we first create a dictionary name_dict with key-value pairs.

  • Then we extract the values from the dictionary using the .values() method and assign them to a variable new_val.
  • We then use the max() function to find the maximum value from the extracted values. Finally, we print the maximum value which is 56 in this case.
Python find max value in a dictionary by using max and dict
Python find max value in a dictionary by using max and dict

Read: How to create an empty Python dictionary

Python find max value in a nested dictionary

In this Python section, we will learn how to find the max value in a dictionary within the dictionary.

# Create a nested dictionary 
my_dictionary = {'Micheal' : {'i' : 15, 'z' : 14},
			'George' : {'q' : 2, 'y' : 10, 'w' : 3},
			'John' : {'n' : 19}}

# Create a empty dictionary to store the result
new_out = {}

# Iterate over the outer dictionary keys and values
for new_k, new_v in my_dictionary.items():
    count_new = 0
    # Iterate over the inner dictionary values
    for element in new_v.values():
        # Check if current value is greater than the previous maximum
        if element > count_new:
            count_new = element
    # Assign the maximum value to the outer dictionary key
    new_out[new_k] = count_new

# Print the final dictionary with maximum values
print(new_out)

In the above code, we first create a nested dictionary my_dictionary with multiple keys, each key having its own dictionary as a value.

  • We then create an empty dictionary new_out to store the result. We use a for loop to iterate over the outer dictionary keys and values, and another for loop to iterate over the values of the inner dictionary.
  • We compare each value of the inner dictionary with a variable count_new, updating the variable if the current value is greater than the previous maximum.
  • Then we assign the maximum value to the outer dictionary key by using this key as the key for the new_out dictionary and the maximum value as the value for this key.
Python find max value in a nested dictionary
Python find max value in a nested dictionary

Read: Python Dictionary to CSV

Python find max value in a dictionary of lists

In this Python section, we will discuss how to find the max value in a dictionary containing the list.

# Create a dictionary with some key-value pairs
dict_new = {'USA': [17,27,81], 'United Kingdom': [19,61,92]}

# Use max() and list comprehension to find the maximum value in the dictionary
new_val = max((max(dict_new[key]) for key in dict_new))

# Print the maximum value
print(new_val)

In the above code, we first create a dictionary dict_new with key-value pairs.

  • Then we use the max() function and list comprehension to find the maximum value in the dictionary.
  • The list comprehension iterates over the keys of the dictionary and for each key, it finds the maximum value in the corresponding list using the max() function.
  • Finally, we print the maximum value which is 92 in this case.
Python find max value in a dictionary of lists
Python find max value in a dictionary of lists

You may also like to read the following tutorials on Python dictionary:

  • Python dictionary pop
  • Python dictionary get() method [With Examples]
  • Python dictionary Copy
  • Python dictionary contains
  • Python dictionary multiple keys

In this Python tutorial, we have discussed the Python find max value in a dictionary. Also, we have covered the following methods:

  • Using dict.items()
  • Using max() and lambda function
  • Using max() and dict()

Bijay Kumar MVP

Python is one of the most popular languages in the United States of America. I have been working with Python for a long time and I have expertise in working with various libraries on Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… I have experience in working with various clients in countries like United States, Canada, United Kingdom, Australia, New Zealand, etc. Check out my profile.

Вступление

В этом руководстве мы рассмотрим, как найти максимальный элемент нескольких распространенных структур данных в Python, таких как список, словарь и кортеж.

Метод max(), встроенный в пространство имен Python, творит чудеса для встроенных типов.

Как получить максимальный элемент списка Python

Список – это встроенный тип Python, который используется для последовательного хранения нескольких ссылок в одном объекте в памяти.

По сравнению с другими языками программирования, список Python по сути представляет собой простой массив. Элементы индексируются на основе их положения в списке, и может быть несколько элементов с одинаковым значением.

Основное отличие в том, что списки в Python могут содержать элементы разных типов. Они разнородны.

# List of different type elements 
example_list = ["string", 5, "five", 4, "4"]

Примечание: если элементы не сопоставимы с помощью операторов сравнения (<,>,==,!=), функция max() не будет работать. Таким образом, мы убедимся, что список однороден, прежде чем пытаться найти максимальный элемент.

Пока вы правильно сравниваете элементы, вы можете найти максимальный элемент независимо от типа. Большую часть времени вы будете работать с целыми числами:

integer_list = [24, 9, 20, 17, 201, 16, 7]

Самый простой способ получить максимальный элемент списка – использовать встроенный метод max():

max_element = max(integer_list)
print("Max element of a list: ", max_element)

Ожидаемый результат:

Max element: 201

Вы можете сравнить строки лексикографически и найти лексикографически наибольшую строку в списке с помощью функции max():

string_list = ["string", "five",  "4"]
max_element = max(string_list)

print("Max element:", max_element)

Результат:

Max element: string

Другой способ найти максимальный элемент списка – отсортировать его с помощью метода sort(), а затем получить последний элемент отсортированного списка, поскольку метод sort() сортирует список в порядке возрастания:

integer_list = [24, 9, 20, 17, 201, 16, 7]
integer_list.sort()
# myList = [7, 9, 16, 17, 20, 24, 201]
max_element = integer_list[-1]

print("Max element of a list: ", max_element)

Этот код также будет иметь тот же результат:

Max element of a list: 201

Если мы также хотим найти индекс элемента max, самый простой способ – использовать встроенный метод index():

integer_list = [24, 9, 20, 17, 201, 16, 7]

max_element = max(integer_list)
max_element_index = integer_list.index(max_element)

print("Max element of a list: ", max_element, " at index: ", max_element_index)

Результат:

Max element of a list:  201  at index:  4

Как получить максимальный элемент словаря Python

Словари в Python используются для хранения пар ключ-значение. Пары с одним и тем же ключом не допускаются, и, начиная с Python 3.7, пары в словаре считаются упорядоченными.

Словари определяются списком пар key-value между парой фигурных скобок:

dictionary = {
    "key24": 24, 
    "key7": 9,
    "key20": 201,
    "key17": 17, 
    "key201": 201, 
}

Самый простой способ получить значение элемента max словаря также заключается в использовании встроенного метода max() со списком значений, передаваемых в качестве аргумента:

max_element = max(dictionary.values())
print("Max element of a dict: ", max_element)

Всё сводится к предыдущему методу, поскольку values() возвращает значения, хранящиеся в списке. Это даст правильный результат:

Max element of a dict: 201

Если вы хотите найти ключ первого элемента с максимальным значением, самый простой способ – использовать метод max(), предоставляющий словарь и извлекающий элемент через dictionary.get().

max_val = max(dictionary.values())
max_val_key = max(dictionary, key=dictionary.get)

print("Max element of a dict:", max_val, "with the key:", max_val_key)

Так мы выведем значение элемента max и первого соответствующего ключа:

Max element of a dict: 201 with the key: key20

Примечание: у вас может возникнуть соблазн использовать max(dictionary), чтобы найти ключ с максимальным значением. Однако так вы вернёте сам максимальный ключ. В нашем случае программа вернула бы ключ с максимальным лексикографическим значением в словаре.

Как получить максимальный элемент кортежа

Кортеж – это встроенный тип Python, последовательно хранящий ссылки на несколько объектов в памяти. Они во многом похожи на списки. Различие лишь в том, что кортеж – это неизменяемая структура данных, в отличие от списка.

Обычно они используются для хранения только нескольких результатов, в виде типов возвращаемых функций.

В Python мы описываем кортежи с помощью пары скобок:

# Tuple of different element types 
exampleTuple = ("string", 5, "five", 4, "4")

Вы можете запускать метод max() только для совместимых типов данных:

int_tuple = (24, 9, 20, 17, 201, 16, 7)
string_tuple = ('one', 'two', 'three')

Вероятно, самый простой способ получить максимальный элемент кортежа – использовать встроенный метод max():

int_tuple = (24, 9, 20, 17, 201, 16, 7)
string_tuple = ('one', 'two', 'three')

max_int = max(int_tuple)
print("Max element of a tuple: ", max_int)

max_str = max(string_tuple)
print("Max element of a tuple: ", max_str)

Опять-таки, это приводит к наибольшему целому числу и лексикографически наибольшей строке:

Max element of a tuple:  201
Max element of a tuple:  two

Заключение

Поиск максимального элемента структуры данных – довольно распространенная задача. Все стандартные структуры данных в Python имеют аналогичный способ поиска элемента max – полагаясь на метод max() во всех случаях.

В этом руководстве мы рассмотрели, как найти максимальный элемент нескольких наиболее популярных структур данных в Python, принимая во внимание особенности каждой из них.

Просмотры: 9 111

In this tutorial, you’ll learn how to use Python to get the dictionary key with max value in a given dictionary, including if multiple keys have the same value. You’ll also learn how to simply get the max value of all keys in a dictionary. You’ll learn how to do this using the operator library, the max() function, and with dictionary comprehensions. You’ll also learn the benefits and the drawbacks of each of these approaches.

Let’s get started!

The Quick Answer: Use the max() function to get the dictionary key with the max values

Quick Answer - Python Dictionary Get Max Value

What are Python Dictionaries?

Dictionaries in Python are one of the main, built-in data structures. They are collections of items, each consisting of a key:value pairs. Python dictionaries are optimized to retrieve values, when the corresponding dictionary key is known.

Values themselves can be repeated, however keys must be unique. Values can also be of any data type (including other dictionaries), while keys must be immutable data types (such as strings, numbers, or tuples).

Let’s take a look at how dictionaries look in Python. They’re created using {} curly brackets and the key:value pairs are separated by commas.

Let’s create a dictionary called ages, which, well, contains the ages of different people:

ages = {
    'Matt': 30,
    'Katie': 29,
    'Nik': 31,
    'Jack': 43,
    'Alison': 32,
    'Kevin': 38
}

We can then access a dictionary item, either by using [] square bracket notation or, better yet, using the .get() dictionary method. Let’s see how we can get the age for Nik:

>> print(ages.get('Nik'))
31

Now that we’ve covered some of the basics of Python dictionaries, let’s take a look at how we can find the max value of a Python dictionary.

The simplest way to get the max value of a Python dictionary is to use the max() function. The function allows us to get the maximum value of any iterable.

Let’s see how it works with a list, before diving into a more complex example with a Python dictionary:

some_list = [30, 29, 31, 43, 32, 38]
max_value = max(some_list)
print(max_value)

# Returns: 43

What we can see here, is that we’ve passed in an iterable, a list, and were able to return max value of that iterable.

But how does this work with dictionaries?

Let’s give it a try just by passing in the dictionary:

max_value = max(ages)
print(max_value)

# Returns: Nik

This isn’t exactly what we’d expected. We were hoping to return 43, or at least a number!

Python dictionaries come built-in with a .values() method, which extracts the values of our list. If you have a keen eye, you’ll notice that our some_list list contains all the values of our dictionary. We can simply pass in our .values() method into the max function.

Let’s take a look!

max_value = max(ages.values())
print(max_value)

# Returns: 43

What we’ve done here is first extracted all the values from our dictionary, and then passed that iterable into our max() function.

Now let’s take a look at how you can return the corresponding key with a max value in Python!

Check out some other Python tutorials on datagy.io, including our complete guide to styling Pandas and our comprehensive overview of Pivot Tables in Pandas!

How To Get Dictionary Key with the Max Value in Python

One helpful skill to learn when working with Python dictionaries is how to get the dictionary key that corresponds with the highest value.

The Python max() function actually accepts a parameter to make this much easier: the key= parameter. The way that this parameter works is to define a function that returns a value for each element of the iterable. So, we can simply pass in a function to compare against!

We can use the .get() method we covered earlier to get the max value of a dictionary in Python. You may recall, from the earlier recap of Python dictionaries, that the .get() method is used to return the value for a key. Let’s see what applying this function to our key= parameter does:

ages = {
    'Matt': 30,
    'Katie': 29,
    'Nik': 31,
    'Jack': 43,
    'Alison': 32,
    'Kevin': 38
}

max_value = max(ages, key=ages.get)
print(max_value)

# Jack

We can see here that by passing in key=ages.get that we return the key with the highest value in a Python dictionary.

How to Get Multiple Dictionary Keys with the Max Values in Python

There may be many times when you want to return the key that has the highest value in a Python dictionary. But what if you dictionary has multiple keys that have the highest value?

Unfortunately, the max() function will simply return the first key it finds.

Fortunately, we can find some alternative solutions to this problem!

We can break down our problem as below:

  1. Get the max value
  2. Create a list comprehension that includes a dictionary key if the key’s value is equal to the max value

Let’s see how we can do this:

ages = {
    'Matt': 30,
    'Katie': 29,
    'Nik': 31,
    'Jack': 43,
    'Jill': 43,
    'Alison': 32,
    'Kevin': 38
}

max_keys = [key for key, value in ages.items() if value == max(ages.values())]

print(max_keys)

# Returns: ['Jack', 'Jill']

In the code above, we loop over the key:value pairs in our dictionary and see if the value is equal to the maximum value. If that’s the case, we add it to our list.

Want to learn more? Check out my in-depth tutorial on Python list comprehensions to learn all you need to know! Or, check out my video on the topic below:

How to Get the Max Value From a List of Dictionaries in Python

You may find yourself working often, with lists of dictionaries. In these cases, it can be helpful to know how to get the max value, across all dictionaries in that list of dictionaries.

Doing this is quite easy! We’ll first do this with a for-loop method, followed by a list comprehension. Let’s take a look at the for-loop method first:

ages = [{'Matt': 30, 'Katie': 29}, {'Nik': 31, 'Jack': 43,}, {'Alison': 32, 'Kevin': 38}]

max_age = int()

for dict in ages:
    if max(dict.values()) > max_age:
        max_age = max(dict.values())

print(max_age)

# Returns 43

We can also re-write this as a list comprehension:

ages = [{'Matt': 30, 'Katie': 29}, {'Nik': 31, 'Jack': 43,}, {'Alison': 32, 'Kevin': 38}]

max_age = max([max(dict.values()) for dict in ages])
print(max_age)

# Returns: 43

Conclusion

In this post, you learned how to get the max value from a dictionary in Python. In addition, you learned how to get the corresponding key or keys that have the max value in a dictionary. Finally, you learned how to get the max value from a list of Python dictionaries.

To learn more about the Python .get() method, check out the official documentation here.

Additional Resources

To learn more about related topics, check out these tutorials:

  • Python Dictionaries: A Complete Overview
  • Python: Add Key:Value Pair to Dictionary
  • Python Defaultdict: Overview and Examples
  • Python: Sort a Dictionary by Values

Python’s built-in min() and max() functions come in handy when you need to find the smallest and largest values in an iterable or in a series of regular arguments. Even though these might seem like fairly basic computations, they turn out to have many interesting use cases in real-world programing. You’ll try out some of those use cases here.

In this tutorial, you’ll learn how to:

  • Use Python’s min() and max() to find smallest and largest values in your data
  • Call min() and max() with a single iterable or with any number of regular arguments
  • Use min() and max() with strings and dictionaries
  • Tweak the behavior of min() and max() with the key and default arguments
  • Use comprehensions and generator expressions as arguments to min() and max()

Once you have this knowledge under your belt, then you’ll be prepared to write a bunch of practical examples that will showcase the usefulness of min() and max(). Finally, you’ll code your own versions of min() and max() in pure Python, which can help you understand how these functions work internally.

To get the most out of this tutorial, you should have some previous knowledge of Python programming, including topics like for loops, functions, list comprehensions, and generator expressions.

Getting Started With Python’s min() and max() Functions

Python includes several built-in functions that make your life more pleasant and productive because they mean you don’t need to reinvent the wheel. Two examples of these functions are min() and max(). They mostly apply to iterables, but you can use them with multiple regular arguments as well. What’s their job? They take care of finding the smallest and largest values in their input data.

Whether you’re using Python’s min() or max(), you can use the function to achieve two slightly different behaviors. The standard behavior for each is to return the minimum or maximum value through straightforward comparison of the input data as it stands. The alternative behavior is to use a single-argument function to modify the comparison criteria before finding the smallest and largest values.

To explore the standard behavior of min() and max(), you can start by calling each function with either a single iterable as an argument or with two or more regular arguments. That’s what you’ll do right away.

Calling min() and max() With a Single Iterable Argument

The built-in min() and max() have two different signatures that allow you to call them either with an iterable as their first argument or with two or more regular arguments. The signature that accepts a single iterable argument looks something like this:

min(iterable, *[, default, key]) -> minimum_value

max(iterable, *[, default, key]) -> maximum_value

Both functions take a required argument called iterable and return the minimum and maximum values respectively. They also take two optional keyword-only arguments: default and key.

Here’s a summary of what the arguments to min() and max() do:

Argument Description Required
iterable Takes an iterable object, like a list, tuple, dictionary, or string Yes
default Holds a value to return if the input iterable is empty No
key Accepts a single-argument function to customize the comparison criteria No

Later in this tutorial, you’ll learn more about the optional default and key arguments. For now, just focus on the iterable argument, which is a required argument that leverages the standard behavior of min() and max() in Python:

>>>

>>> min([3, 5, 9, 1, -5])
-5

>>> min([])
Traceback (most recent call last):
    ...
ValueError: min() arg is an empty sequence

>>> max([3, 5, 9, 1, -5])
9

>>> max([])
Traceback (most recent call last):
    ...
ValueError: max() arg is an empty sequence

In these examples, you call min() and max() with a list of integer numbers and then with an empty list. The first call to min() returns the smallest number in the input list, -5. In contrast, the first call to max() returns the largest number in the list, or 9. If you pass an empty iterator to min() or max(), then you get a ValueError because there’s nothing to do on an empty iterable.

An important detail to note about min() and max() is that all the values in the input iterable must be comparable. Otherwise, you get an error. For example, numeric values work okay:

>>>

>>> min([3, 5.0, 9, 1.0, -5])
-5

>>> max([3, 5.0, 9, 1.0, -5])
9

These examples combine int and float numbers in the calls to min() and max(). You get the expected result in both cases because these data types are comparable.

However, what would happen if you mixed strings and numbers? Check out the following examples:

>>>

>>> min([3, "5.0", 9, 1.0, "-5"])
Traceback (most recent call last):
    ...
TypeError: '<' not supported between instances of 'str' and 'int'

>>> max([3, "5.0", 9, 1.0, "-5"])
Traceback (most recent call last):
    ...
TypeError: '>' not supported between instances of 'str' and 'int'

You can’t call min() or max() with an iterable of noncomparable types as an argument. In this example, a function tries to compare a number to a string, which is like comparing apples and oranges. The end result it that you get a TypeError.

Calling min() and max() With Multiple Arguments

The second signature of min() and max() allows you to call them with any number of arguments, provided that you use at least two arguments. This signature has the following form:

min(arg_1, arg_2[, ..., arg_n], *[, key]) -> minimum_value

max(arg_1, arg_2[, ..., arg_n], *[, key]) -> maximum_value

Again, these functions return the minimum and maximum values, respectively. Here’s the meaning of the arguments in the above signature:

Argument Description Required
arg_1, arg_2, ..., arg_n Accepts any number of regular arguments to compare Yes (at least two of them)
key Takes a single-argument function to customize the comparison criteria No

This variation of min() or max() doesn’t have a default argument. You must provide at least two arguments in the call for the function to work correctly. So, a default value isn’t required, because you’ll always have at least two values to compare in order to find the minimum or maximum.

To try out this alternative signature, run the following examples:

>>>

>>> min(3, 5, 9, 1, -5)
-5

>>> max(3, 5, 9, 1, -5)
9

You can call min() or max() with two or more regular arguments. Again, you’ll get the minimum or maximum value in the input data, respectively. The only condition is that the arguments must be comparable.

Using min() and max() With Strings and Iterables of Strings

By default, min() and max() can process values that are comparable. Otherwise, you get a TypeError, as you’ve already learned. Up to this point, you’ve seen examples that use numeric values either in an iterable or as multiple regular arguments.

Using min() and max() with numeric values is arguably the most common and useful use case of these functions. However, you can also use the functions with strings and iterables of strings. In these cases, the alphabetical order of characters will decide the final result.

For example, you can use min() and max() to find the smallest and largest letters in some text. In this context, smallest means closest to the beginning of the alphabet, and largest means closest to the end of the alphabet:

>>>

>>> min("abcdefghijklmnopqrstuvwxyz")
'a'

>>> max("abcdefghijklmnopqrstuvwxyz")
'z'

>>> min("abcdWXYZ")
'W'

>>> max("abcdWXYZ")
'd'

As promised, in the first two examples, min() returns 'a' and max() returns 'z'. However, in the second pair of examples, min() returns 'W' and max() returns 'd'. Why? Because uppercase letters come before lowercase letters in Python’s default character set, UTF-8.

Using min() or max() with a string as an argument isn’t limited to just letters. You can use strings containing any possible characters in your current character set. For example, if you’re working with the set of ASCII characters only, then the smallest character is the character closest to the beginning of the ASCII table. In contrast, the largest character is the character closest to the end of the table.

With other character sets like UTF-8, min() and max() behave similarly:

>>>

>>> # UTF-8 characters

>>> min("abc123ñ")
'1'

>>> max("abc123ñ")
'ñ'

Behind the scenes, min() and max() use the character’s numeric value to find the minimum and maximum characters in the input string. For example, in the Unicode character table, the uppercase A has a smaller numeric value than the lowercase a:

>>>

>>> ord("A")
65

>>> ord("a")
97

Python’s built-in ord() function takes a single Unicode character and returns an integer representing the Unicode code point of that character. In these examples, the code point for the uppercase "A" is lower than the code point for the lowercase "a".

This way, when you call min() and max() with both letters, you get results that match the order of the underlying Unicode code points of these letters:

>>>

>>> min("aA")
'A'

>>> max("aA")
'a'

What makes "A" smaller than "a"? The quick answer is the letter’s Unicode code point. All characters that you can type on your keyboard, and many other characters, have their own code points in the Unicode table. Python uses these code points to determine the minimum and maximum character when it comes to using min() and max().

Finally, you can also call min() and max() with iterables of strings or with multiple string arguments. Again, both functions will determine their return value by comparing the strings alphabetically:

>>>

>>> min(["Hello", "Pythonista", "and", "welcome", "world"])
'Hello'

>>> max(["Hello", "Pythonista", "and", "welcome", "world"])
'world'

To find the smallest or largest string in an iterable of strings, min() and max() compare all the strings alphabetically based on the code points of initial characters.

In the first example, the uppercase "H" comes before "P", "a", and "w" in the Unicode table. So, min() immediately concludes that "Hello" is the smallest string. In the second example, the lowercase "w" comes after all the other strings’ initial letters.

Note that there are two words that start with "w", "welcome" and "world". So, Python proceeds to look at the second letter of each word. The result is that max() returns "world" because "o" comes after "e".

Processing Dictionaries With min() and max()

When it comes to processing Python dictionaries with min() and max(), you need to consider that if you use the dictionary directly, then both functions will operate on the keys:

>>>

>>> prices = {
...    "banana": 1.20,
...    "pineapple": 0.89,
...    "apple": 1.57,
...    "grape": 2.45,
... }


>>> min(prices)
'apple'

>>> max(prices)
'pineapple'

In these examples, min() returns the alphabetically smallest key in prices, and max() returns the largest one. You can get the same result using the .keys() method on your input dictionary:

>>>

>>> min(prices.keys())
'apple'

>>> max(prices.keys())
'pineapple'

The only difference between this latter example and the previous one is that here, the code is more explicit and clear about what you’re doing. Anyone reading your code will quickly realize that you want to find the smallest and largest keys in the input dictionary.

Another common requirement would be to find the smallest and largest values in a dictionary. To continue with the prices example, say you want to know the smallest and largest prices. In this situation, you can use the .values() method:

>>>

>>> min(prices.values())
0.89

>>> max(prices.values())
2.45

In these examples, min() goes through all the values in prices and finds the minimum price. Similarly, max() iterates over the values of prices and returns the maximum price.

Finally, you can also use the .items() method on the input dictionary to find the minimum and maximum key-value pairs:

>>>

>>> min(prices.items())
('apple', 1.57)

>>> max(prices.items())
('pineapple', 2.45)

In this case, min() and max() use Python’s internal rules to compare tuples and find the smallest and largest items in the input dictionary.

Python compares tuples item by item. For example, to determine if (x1, x2) is greater than (y1, y2), Python tests x1 > y1. If this condition is True, then Python concludes that the first tuple is greater than the second without checking the rest of the items. In contrast, if x1 < y1, then Python concludes that the first tuple is less than the second.

Finally, if x1 == y1, then Python compares the second pair of items using the same rules. Note that in this context, the first item of each tuple comes from the dictionary keys, and because dictionary keys are unique, the items can’t be equal. So, Python will never have to compare the second values.

Tweaking the Standard Behavior of min() and max() With key and default

Up to this point, you’ve learned how min() and max() work in their standard form. In this section, you’ll learn how to tweak the standard behavior of both functions by using the key and default keyword-only arguments.

The key argument to min() or max() allows you to provide a single-argument function that will be applied to every value in the input data. The goal is to modify the comparison criteria to use in finding the minimum or maximum value.

As an example of how this feature can be useful, say that you have a list of numbers as strings, and want to find the smallest and largest numbers. If you process the list directly with min() and max(), then you get the following results:

>>>

>>> min(["20", "3", "35", "7"])
'20'

>>> max(["20", "3", "35", "7"])
'7'

These may not be the results that you need or expect. You’re getting the smallest and largest strings based on Python’s string comparison rules rather than based on the actual numeric value of each string.

In that case, the solution is to pass the built-in int() function as the key argument to min() and max(), like in the following examples:

>>>

>>> min(["20", "3", "35", "7"], key=int)
'3'

>>> max(["20", "3", "35", "7"], key=int)
'35'

Great! Now the result of min() or max() depends on the numeric values of the underlying strings. Note that you don’t need to call int(). You just pass int without the pair of parentheses because key expects a function object, or more accurately, a callable object.

The second keyword-only argument that allows you to customize the standard behavior of min() or max() is default. Remember that this argument is only available when you call the function with a single iterable as an argument.

The job of default is to provide a suitable default value as the return value of min() or max() when it’s called with an empty iterable:

>>>

>>> min([], default=42)
42

>>> max([], default=42)
42

In these examples, the input iterable is an empty list. The standard behavior is for min() or max() to raise a ValueError complaining about the empty sequence argument. However, because you supply a value to default, both functions now return this value instead of raising an exception and breaking your code.

Using min() and max() With Comprehensions and Generator Expressions

You can also call min() or max() with a list comprehension or generator expression as an argument. This feature comes in handy when you need to transform the input data right before finding the minimum or maximum transformed value.

When you feed a list comprehension into min() or max(), the resulting value will come from the transformed data rather than from the original data:

>>>

>>> letters = ["A", "B", "C", "X", "Y", "Z"]

>>> min(letters)
'A'
>>> min([letter.lower() for letter in letters])
'a'

>>> max(letters)
'Z'
>>> max([letter.lower() for letter in letters])
'z'

The second call to min() takes a list comprehension as an argument. This comprehension transforms the original data in letters by applying the .lower() method to each letter. The final result is the lowercase "a", which isn’t present in the original data. Something similar happens with the examples covering max().

Note that using min() or max() with a list comprehension is similar to using the key argument. The main difference is that with comprehensions, the final result is a transformed value, while with key, the result comes from the original data:

>>>

>>> letters = ["A", "B", "C", "X", "Y", "Z"]

>>> min([letter.lower() for letter in letters])
'a'

>>> min(letters, key=str.lower)
'A'

In both examples, min() uses .lower() to somehow modify the comparison criteria. The difference is that the comprehension actually transforms the input data before doing the computation, so the resulting value comes from the transformed data rather than from the original.

List comprehensions create a complete list in memory, which is often a wasteful operation. This fact holds especially true if you don’t need the resulting list in your code anymore, which could be the case with min() and max(). So, it’s always more efficient to use a generator expression instead.

The syntax for generator expressions is almost the same as for list comprehensions:

>>>

>>> letters = ["A", "B", "C", "X", "Y", "Z"]

>>> min(letters)
'A'
>>> min(letter.lower() for letter in letters)
'a'

>>> max(letters)
'Z'
>>> max(letter.lower() for letter in letters)
'z'

The main syntax difference is that a generator expression uses parentheses instead of square brackets ([]). Because a function call already requires parentheses, you just need to remove the square brackets from your comprehension-based examples, and you’re good to go. Unlike list comprehensions, generator expressions yield items on demand, which makes them memory efficient.

Putting Python’s min() and max() Into Action

So far, you’ve learned the basics of using min() and max() to find the smallest and largest values in an iterable or in a series of individual values. You learned how min() and max() work with different built-in Python data types, such as numbers, strings, and dictionaries. You also explored how to tweak the standard behavior of these functions and how to use them with list comprehensions and generator expressions.

Now you’re ready to start coding a few practical examples that will show you how to use min() and max() in your own code.

Removing the Smallest and Largest Numbers in a List

To kick things off, you’ll start with a short example of how to remove the minimum and maximum values from a list of numbers. To do that, you can call .remove() on your input list. Depending on your needs, you’ll use min() or max() to select the value that you’ll remove from the underlying list:

>>>

>>> sample = [4, 5, 7, 6, -12, 4, 42]

>>> sample.remove(min(sample))
>>> sample
[4, 5, 7, 6, 4, 42]

>>> sample.remove(max(sample))
>>> sample
[4, 5, 7, 6, 4]

In these examples, the minimum and maximum values in sample could be outlier data points that you want to remove so that they don’t affect your further analysis. Here, min() and max() provide the arguments to .remove().

Building Lists of Minimum and Maximum Values

Now say that you have a list of lists representing a matrix of numeric values, and you need to build lists containing the smallest and largest values from every row in the input matrix. To do this, you can use min() and max() along with a list comprehension:

>>>

>>> matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

>>> [min(x) for x in matrix]
[1, 4, 7]

>>> [max(x) for x in matrix]
[3, 6, 9]

The first comprehension iterates over the sublists in matrix and uses min() to build a list containing the smallest value from each sublist. The second comprehension does a similar task but uses max() to create a list containing the largest values from the sublists in matrix.

Even though min() and max() provide a quick way to deal with the examples in this section, the NumPy library is highly recommended when it comes to processing matrixes in Python because NumPy has specific and optimized tools for the job.

Clipping Values to the Edges of an Interval

Sometimes you have a list of numeric values and want to clip them to the edges or limits of a given interval. For example, if a given value is greater than the interval’s upper limit, then you need to convert it down to that limit. To do this operation, you can use min().

Wait! Why min()? You’re dealing with the large values, aren’t you? The point is that you need to compare each large value to the interval’s upper limit and then choose the smaller of the two. You’ll essentially set all large values to a prescribed upper limit:

>>>

>>> # Clip values to the largest interval's edge

>>> upper = 100
>>> numbers = [42, 78, 200, -230, 25, 142]

>>> [min(number, upper) for number in numbers]
[42, 78, 100, -230, 25, 100]

The call to min() compares every number to the interval’s upper limit. If the target number is greater than the limit, then min() returns the limit. The net effect is that all the values that are greater than the limit are now clipped to it. In this example, the numbers 200 and 142 are clipped to 100, which is the interval’s upper limit.

In contrast, if you want to clip small values to the interval’s lower limit, then you can use max(), like in the following example:

>>>

>>> # Clip values to the smallest interval's edge

>>> lower = 10
>>> numbers = [42, 78, 200, -230, 25, 142]

>>> [max(number, lower) for number in numbers]
[42, 78, 200, 10, 25, 142]

This call to max() clips the small values to the interval’s lower limit. To do this clipping, max() compares the current number and the interval’s limit to find the maximum value. In the example, -230 is the only number that gets clipped.

Finally, you can run both operations in one go by combining min() and max(). Here’s how to do it:

>>>

>>> # Clipping values to 10 - 100

>>> lower, upper = 10, 100
>>> numbers = [42, 78, 100, -230, 25, 142]

>>> [max(min(number, upper), lower) for number in numbers]
[42, 78, 100, 10, 25, 100]

To clip all the values that fall outside the interval’s limits, this comprehension combines min() and max(). The call to min() compares the current value to the interval’s upper limit, while the call to max() compares the result to the lower limit. The final result is that values lower than or greater than the corresponding limit are clipped to the limit itself.

This comprehension works similarly to the clip() function from NumPy, which takes an array and the limits of the target interval, then it clips all values outside the interval to the interval’s edges.

Finding the Closest Points

Now say that you have a list of tuples containing pairs of values that represent Cartesian points. You want to process all these pairs of points and find out which pair has the smallest distance between points. In this situation, you can do something like the following:

>>>

>>> import math

>>> point_pairs = [
...     ((12, 5), (9, 4)),
...     ((2, 5), (3, 7)),
...     ((4, 11), (15, 2))
... ]

>>> min(point_pairs, key=lambda points: math.dist(*points))
((2, 5), (3, 7))

In this example, you first import math to get access to dist(). This function returns the Euclidean distance between two points, p and q, each given as a sequence of coordinates. The two points must have the same number of dimensions.

The min() function works its magic through its key argument. In this example, key takes a lambda function that computes the distance between two points. This function becomes the comparison criteria for min() to find the pair of points with the minimal distance between points.

In this example, you need a lambda function because key expects a single-argument function, while math.dist() requires two arguments. So, the lambda function takes a single argument, points, and then unpacks it into two arguments to feed into math.dist().

Identifying Cheap and Expensive Products

Now say you have a dictionary with the names and prices of several products, and you want to identify the cheapest and most expensive products. In this situation, you can use .items() and an appropriate lambda function as the key argument:

>>>

>>> prices = {
...    "banana": 1.20,
...    "pineapple": 0.89,
...    "apple": 1.57,
...    "grape": 2.45,
... }

>>> min(prices.items(), key=lambda item: item[1])
('pineapple', 0.89)

>>> max(prices.items(), key=lambda item: item[1])
('grape', 2.45)

In this example, the lambda function takes a key-value pair as an argument and returns the corresponding value so that min() and max() have proper comparison criteria. As a result, you get a tuple with the cheapest and most expensive products in the input data.

Finding Coprime Integer Numbers

Another interesting example of using min() to solve a real-world problem is when you need to figure out if two numbers are coprime. In other words, you need to know if your numbers’ only common divisor is 1.

In that situation, you can code a Boolean-valued or predicate function like the following:

>>>

>>> def are_coprime(a, b):
...     for i in range(2, min(a, b) + 1):
...         if a % i == 0 and b % i == 0:
...             return False
...     return True
...

>>> are_coprime(2, 3)
True
>>> are_coprime(2, 4)
False

In this code snippet, you define are_coprime() as a predicate function that returns True if the input numbers are coprime. If the numbers aren’t coprime, then the function returns False.

The function’s main component is a for loop that iterates over a range of values. To set the upper limit for this range object, you use min() with the input numbers as arguments. Again, you’re using min() to set the upper limit of some interval.

Timing Different Implementations of Your Code

You can also use min() to compare several of your algorithms, evaluate their execution times, and determine which algorithm is the most efficient. The example below uses timeit.repeat() to measure the execution times for two different ways of building a list containing the square values of the numbers from 0 to 99:

>>>

>>> import timeit

>>> min(
...     timeit.repeat(
...         stmt="[i ** 2 for i in range(100)]",
...         number=1000,
...         repeat=3
...     )
... )
0.022141209003166296

>>> min(
...     timeit.repeat(
...         stmt="list(map(lambda i: i ** 2, range(100)))",
...         number=1000,
...         repeat=3
...     )
... )
0.023857666994445026

The call to timeit.repeat() runs a string-based statement a given number of times. In these examples, the statement is repeated three times. The call to min() returns the smallest execution time from the three repetitions.

By combining min(), repeat(), and other Python timer functions, you can get an idea of which of your algorithms is most efficient in terms of execution time. The example above shows that list comprehensions can be a little bit faster than the built-in map() function when it comes to building new lists.

Exploring the Role of .__lt__() and .__gt__() in min() and max()

As you’ve learned so far, the built-in min() and max() functions are versatile enough to work with values of various data types, such as numbers and strings. The secret behind this flexibility is that min() and max() embrace Python’s duck typing philosophy by relying on the .__lt__() and .__gt__() special methods.

These methods are part of what Python calls rich comparison methods. Specifically, .__lt__() and .__gt__() support the less than (<) and greater than (>) operators, respectively. What’s the meaning of support here? When Python finds something like x < y in your code, it internally does x.__lt__(y).

The takeaway is that you can use min() and max() with values of any data type that implements .__lt__() and .__gt__(). That’s why these functions work with values of all Python’s built-in data types:

>>>

>>> "__lt__" in dir(int) and "__gt__" in dir(int)
True

>>> "__lt__" in dir(float) and "__gt__" in dir(float)
True

>>> "__lt__" in dir(str) and "__gt__" in dir(str)
True

>>> "__lt__" in dir(list) and "__gt__" in dir(list)
True

>>> "__lt__" in dir(tuple) and "__gt__" in dir(tuple)
True

>>> "__lt__" in dir(dict) and "__gt__" in dir(dict)
True

Python’s built-in data types implement the .__lt__() and .__gt__() special methods. So, you can feed any of these data types into min() and max(), with the only condition being that the involved data types are comparable.

You can also make instances of your custom classes compatible with min() and max(). To achieve this, you need to provide your own implementations of .__lt__() and .__gt__(). Consider the following Person class as an example of this compatibility:

# person.py

from datetime import date

class Person:
    def __init__(self, name, birth_date):
        self.name = name
        self.birth_date = date.fromisoformat(birth_date)

    def __repr__(self):
        return (
            f"{type(self).__name__}"
            f"({self.name}, {self.birth_date.isoformat()})"
        )

    def __lt__(self, other):
        return self.birth_date > other.birth_date

    def __gt__(self, other):
        return self.birth_date < other.birth_date

Note that the implementation of .__lt__() and .__gt__() requires an argument that’s typically named other. This argument represents the second operand in the underlying comparison operations. For example, in an expression like x < y, you’ll have that x will be self and y will be other.

In this example, .__lt__() and .__gt__() return the result of comparing two people’s .birth_date attributes. Here’s how this works in practice:

>>>

>>> from person import Person

>>> jane = Person("Jane Doe", "2004-08-15")
>>> john = Person("John Doe", "2001-02-07")

>>> jane < john
True
>>> jane > john
False

>>> min(jane, john)
Person(Jane Doe, 2004-08-15)

>>> max(jane, john)
Person(John Doe, 2001-02-07)

Cool! You can process Person objects with min() and max() because the class provides implementation of .__lt__() and .__gt__(). The call to min() returns the youngest person, and the call to max() returns the oldest.

Note that if a given custom class doesn’t provide these methods, then its instances won’t support min() and max() operations:

>>>

>>> class Number:
...     def __init__(self, value):
...         self.value = value
...

>>> x = Number(21)
>>> y = Number(42)

>>> min(x, y)
Traceback (most recent call last):
    ...
TypeError: '<' not supported between instances of 'Number' and 'Number'

>>> max(x, y)
Traceback (most recent call last):
    ...
TypeError: '>' not supported between instances of 'Number' and 'Number'

Because this Number class doesn’t provide suitable implementations of .__lt__() and .__gt__(), min() and max() respond with a TypeError. The error message tells you that the comparison operations aren’t supported in your current class.

Emulating Python’s min() and max()

Up to this point, you’ve learned how Python’s min() and max() functions work. You’ve used them to find the smallest and largest values among several numbers, strings, and more. You know how to call these functions either with a single iterable as an argument or with an undefined number of regular arguments. Finally, you’ve coded a series of practical examples that approach real-world problems using min() and max().

Although Python kindly provides you with min() and max() to find the smallest and largest values in your data, learning how to do this computation from scratch is a helpful exercise that can improve your logical thinking and your programming skills.

In this section, you’ll learn how to find minimum and maximum values in your data. You’ll also learn how to implement your own versions of min() and max().

Understanding the Code Behind min() and max()

To find the minimum value in a small list of numbers as a human, you’d normally check the numbers and implicitly compare all of them in your mind. Yes, your brain is amazing! However, computers aren’t that smart. They need detailed instructions to accomplish any task.

You’ll have to tell your computer to iterate over all the values while comparing them in pairs. In the process, the computer has to take note of the current minimum value in each pair until the list of values is processed entirely.

This explanation may be hard to visualize, so here’s a Python function that does the work:

>>>

>>> def find_min(iterable):
...     minimum = iterable[0]
...     for value in iterable[1:]:
...         if value < minimum:
...             minimum = value
...     return minimum
...

>>> find_min([2, 5, 3, 1, 9, 7])
1

In this code snippet, you define find_min(). This function assumes that iterable isn’t empty and that its values are in an arbitrary order.

The function treats the first value as a tentative minimum. Then the for loop iterates over the rest of the elements in the input data.

The conditional statement compares the current value to the tentative minimum in the first iteration. If the current value is smaller than minimum, then the conditional updates minimum accordingly.

Each new iteration compares the current value to the updated minimum. When the function reaches the end of iterable, minimum will hold the smallest value in the input data.

Cool! You’ve coded a function that finds the smallest value in an iterable of numbers. Now revisit find_min() and think of how you’d code a function to find the largest value. Yes, that’s it! You just have to change the comparison operator from less than (<) to greater than (>), and probably rename the function and some local variables to prevent confusion.

Your new function can look something like this:

>>>

>>> def find_max(iterable):
...     maximum = iterable[0]
...     for value in iterable[1:]:
...         if value > maximum:
...             maximum = value
...     return maximum
...

>>> find_max([2, 5, 3, 1, 9, 7])
9

Note that find_max() shares most of its code with find_min(). The most important difference, apart from naming, is that find_max() uses the greater than operator (>) instead of the less than operator (<).

As an exercise, you can think of how to avoid repetitive code in find_min() and find_max() following the DRY (don’t repeat yourself) principle. This way, you’ll be ready to emulate the complete behavior of min() and max() using your Python skills, which you’ll tackle in just a moment.

Before diving in, you need to be aware of the knowledge requirements. You’ll be combining topics like conditional statements, exception handling, list comprehensions, definite iteration with for loops, and *args and optional arguments in functions.

If you feel that you don’t know everything about these topics, then don’t worry. You’ll learn by doing. If you get stuck, then you can go back and review the linked resources.

Planning Your Custom min() and max() Versions

To write your custom implementations of min() and max(), you’ll start by coding a helper function that’s able to find the smallest or largest value in the input data, depending on the arguments you use in the call. Of course, the helper function will especially depend on the operator used for comparing the input values.

Your helper function will have the following signature:

min_max(*args, operator, key=None, default=None) -> extreme_value

Here’s what each argument does:

Argument Description Required
*args Allows you to call the function with either an iterable or any number of regular arguments Yes
operator Holds the appropriate comparison operator function for the computation at hand Yes
key Takes a single-argument function that modifies the function’s comparison criteria and behavior No
default Stores a default value to return when you call the function with an empty iterable No

The body of min_max() will start by processing *args to build a list of values. Having a standardized list of values will allow you to write the required algorithm to find the minimum and maximum values in the input data.

Then the function needs to deal with the key and default arguments before computing the minimum and maximum, which is the final step inside min_max().

With min_max() in place, the final step is to define two independent functions on top of it. These functions will use appropriate comparison operator functions to find the minimum and maximum values, respectively. You’ll learn more about operator functions in a moment.

Standardizing the Input Data From *args

To standardize the input data, you need to check if the user is providing a single iterable or any number of regular arguments. Fire up your favorite code editor or IDE and create a new Python file called min_max.py. Then add the following piece of code to it:

# min_max.py

def min_max(*args, operator, key=None, default=None):
    if len(args) == 1:
        try:
            values = list(args[0])  # Also check if the object is iterable
        except TypeError:
            raise TypeError(
                f"{type(args[0]).__name__} object is not iterable"
            ) from None
    else:
        values = args

Here, you define min_max(). The function’s first portion standardizes the input data for further processing. Because the user will be able to call min_max() with either a single iterable or with several regular arguments, you need to check the length of args. To do this check, you use the built-in len() function.

If args holds only one value, then you need to check if that argument is an iterable object. You use list(), which implicitly does the check and also turns the input iterable into a list.

If list() raises a TypeError, then you catch it and raise your own TypeError to inform the user that the provided object isn’t iterable, just like min() and max() do in their standard form. Note that you use the from None syntax to hide away the traceback of the original TypeError.

The else branch runs when args holds more than one value, which handles the cases where the user calls the function with several regular arguments instead of with a single iterable of values.

If this conditional doesn’t ultimately raise a TypeError, then values will hold a list of values that may be empty. Even if the resulting list is empty, it’s now clean and ready for continuing the process of finding its minimum or maximum value.

Processing the default Argument

To continue writing min_max(), you can now process the default argument. Go ahead and add the following code to the end of the function:

# min_max.py
# ...

def min_max(*args, operator, key=None, default=None):
    # ...

    if not values:
        if default is None:
            raise ValueError("args is an empty sequence")
        return default

In this code snippet, you define a conditional to check if values holds an empty list. If that’s the case, then you check the default argument to see if the user provided a value for it. If default is still None, then a ValueError is raised. Otherwise, default gets returned. This behavior emulates the standard behavior of min() and max() when you call them with empty iterables.

Handling the Optional key Function

Now you need to process the key argument and prepare the data for finding the smallest and largest values according to the provided key. Go ahead and update min_max() with the following code:

# min_max.py
# ...

def min_max(*args, operator, key=None, default=None):
    # ...

    if key is None:
        keys = values
    else:
        if callable(key):
            keys = [key(value) for value in values]
        else:
            raise TypeError(f"{type(key).__name__} object is not a callable")

You start this code fragment with a conditional that checks if the user hasn’t provided a key function. If they haven’t, then you create a list of keys directly from your original values. You’ll use these keys as comparison keys in computing the minimum and maximum.

On the other hand, if the user has provided a key argument, then you need to make sure that the argument is actually a function or callable object. To do this, you use the built-in callable() function, which returns True if its argument is a callable and False otherwise.

Once you’re sure that key is a callable object, then you build the list of comparison keys by applying key to each value in the input data.

Finally, if key isn’t a callable object, then the else clause runs, raising a TypeError, just like min() and max() do in a similar situation.

Finding Minimum and Maximum Values

The last step to finish your min_max() function is to find the minimum and maximum values in the input data, just like min() and max() do. Go ahead and wrap up min_max() with the following code:

# min_max.py
# ...

def min_max(*args, operator, key=None, default=None):
    # ...

    extreme_key, extreme_value = keys[0], values[0]
    for key, value in zip(keys[1:], values[1:]):
        if operator(key, extreme_key):
            extreme_key = key
            extreme_value = value
    return extreme_value

You set the extreme_key and extreme_value variables to the first value in keys and in values, respectively. These variables will provide the initial key and value for computing the minimum and maximum.

Then you loop over the remaining keys and values in one go using the built-in zip() function. This function will yield key-value tuples by combining the values in your keys and values lists.

The conditional inside the loop calls operator to compare the current key to the tentative minimum or maximum key stored in extreme_key. At this point, the operator argument will hold either lt() or gt() from the operator module, depending on if you want to find the minimum or maximum value, respectively.

For example, when you want to find the smallest value in the input data, operator will hold the lt() function. When you want to find the largest value, operator will hold gt().

Every loop iteration compares the current key to the tentative minimum or maximum key and updates the values of extreme_key and extreme_value accordingly. At the end of the loop, these variables will hold the minimum or maximum key and its corresponding value. Finally, you just need to return the value in extreme_value.

Coding Your Custom min() and max() Functions

With the min_max() helper function in place, you can define your custom versions of min() and max(). Go ahead and add the following functions to the end of your min_max.py file:

# min_max.py

from operator import gt, lt

# ...

def custom_min(*args, key=None, default=None):
    return min_max(*args, operator=lt, key=key, default=default)

def custom_max(*args, key=None, default=None):
    return min_max(*args, operator=gt, key=key, default=default)

In this code snippet, you first import gt() and lt() from the operator module. These functions are the functional equivalent of the greater than (>) and less than (<) operators, respectively. For example, the Boolean expression x < y is equivalent to the function call lt(x, y). You’ll use these functions to provide the operator argument to your min_max().

Just like min() and max(), custom_min() and custom_max() take *args, key, and default as arguments and return the minimum and maximum values, respectively. To perform the computation, these functions call min_max() with the required arguments and with the appropriate comparison operator function.

In custom_min(), you use lt() to find the smallest value in the input data. In custom_max(), you use gt() to get the largest value.

Click the collapsible section below if you want to get the entire content of your min_max.py file:

# min_max.py

from operator import gt, lt

def min_max(*args, operator, key=None, default=None):
    if len(args) == 1:
        try:
            values = list(args[0])  # Also check if the object is iterable
        except TypeError:
            raise TypeError(
                f"{type(args[0]).__name__} object is not iterable"
            ) from None
    else:
        values = args

    if not values:
        if default is None:
            raise ValueError("args is an empty sequence")
        return default

    if key is None:
        keys = values
    else:
        if callable(key):
            keys = [key(value) for value in values]
        else:
            raise TypeError(f"{type(key).__name__} object is not a callable")

    extreme_key, extreme_value = keys[0], values[0]
    for key, value in zip(keys[1:], values[1:]):
        if operator(key, extreme_key):
            extreme_key = key
            extreme_value = value
    return extreme_value

def custom_min(*args, key=None, default=None):
    return min_max(*args, operator=lt, key=key, default=default)

def custom_max(*args, key=None, default=None):
    return min_max(*args, operator=gt, key=key, default=default)

Cool! You’ve finished coding your own versions of min() and max() in Python. Now go ahead and give them a try!

Conclusion

Now you know how to use Python’s built-in min() and max() functions to find the smallest and largest values in an iterable or in a series of two or more regular arguments. You also learned about a few other characteristics of min() and max() that can make them useful in your day-to-day programming.

In this tutorial, you learned how to:

  • Find the smallest and largest values using Python’s min() and max(), respectively
  • Call min() and max() with a single iterable and with several regular arguments
  • Use min() and max() with strings and dictionaries
  • Customize the behavior of min() and max() with key and default
  • Feed comprehensions and generator expressions into min() and max()

Additionally, you’ve coded a handful of practical examples using min() and max() to approach real-world problems that you might run into while coding. You’ve also a written custom version of min() and max() in pure Python, a nice learning exercise that helped you understand the logic behind these built-in functions.

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