Object of type nonetype has no len как исправить

This error occurs when you pass a None value to a len() function call. NoneType objects are returned by functions that do not return anything and do not have a length.

You can solve the error by only passing iterable objects to the len() function. Also, ensure that you do not assign the output from a function that works in-place like sort() to the variable name for an iterable object, as this will override the original object with a None value

In this tutorial, we will explore the causes of this error with code examples, and you will learn how to solve the error in your code.

TypeError: object of type ‘NoneType’ has no len()

We raise a Python TypeError when attempting to perform an illegal operation for a specific type. In this case, the type is NoneType.

The part ‘has no len()‘ tells us the map object does not have a length, and therefore len() is an illegal operation for the NoneType object.

Retrieving the length of an object is only suitable for iterable objects, like a list or a tuple.

The len() method implicitly calls the dunder method __len__() which returns a positive integer representing the length of the object on which it is called. All iterable objects have __len__ as an attribute. Let’s check if __len__ is in the list of attributes for an NoneType object and a list object using the built-in dir() method.

def hello_world():
    print('Hello World')

print(type(hello_world())
print('__len__' in dir(hello_world())

Hello World
<class 'NoneType'>
Hello World
False

We can see that __len__ is not present in the attributes of the NoneType object.

lst = ["football", "rugby", "tennis"]

print(type(lst))

print('__len__' in dir(lst))

<class 'list'>
True

We can see that __len__ is present in the attributes of the list object.

Example #1: Reassigning a List with a Built-in Function

Let’s write a program that sorts a list of dictionaries of fundamental particles. We will sort the list in ascending order of the particle mass. The list will look as follows:

particles = [
    
{"name":"electron", "mass": 0.511},
    {"name":"muon", "mass": 105.66},
    {"name":"tau", "mass": 1776.86},
    {"name":"charm", "mass":1200},
    {"name":"strange", "mass":120}
 ]

Each dictionary contains two keys and values, and one key corresponds to the particle’s name, and the other corresponds to the mass of the particle in MeV. The next step involves using the sort() method to sort the list of particles by their masses.

def particle_sort(p):
     
    return p["mass"]
sorted_particles = particles.sort(key=particle_sort)

The particle_sort function returns the value of “mass” in each dictionary. We use the mass values as the key to sorting the list of dictionaries using the sort() method. Let’s try and print the contents of the original particles list with a for loop:

for p in particles:

    print("{} has a mass of {} MeV".format(p["name"], p["mass"]))

electron has a mass of 0.511 MeV

muon has a mass of 105.66 MeV

strange has a mass of 120 MeV

charm has a mass of 1200 MeV

tau has a mass of 1776.86 MeV

Let’s see what happens when we try to print the length of sorted_particles:

print("There are {} particles in the list".format(len(sorted_particles)))

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-57-9b5c6f8e88b6> in <module>
----> 1 print("There are {} particles in the list".format(len(sorted_particles)))
TypeError: object of type 'NoneType' has no len()

Let’s try and print sorted_particles

print(sorted_particles)

None

Solution

To solve this error, we do not assign the result of the sort() method to sorted_particles. If we assign the sort result, it will change the list in place; it will not create a new list. Let’s see what happens if we remove the declaration of sorted_particles and use particles, and then print the ordered list.

particles.sort(key=particle_sort)
print("There are {} particles in the list".format(len(particles)))
for p in particles:
    print("{} has a mass of {} MeV.".format(p["name"],p["mass"]))

There are 5 particles in the list
electron has a mass of 0.511 MeV.
muon has a mass of 105.66 MeV.
strange has a mass of 120 MeV.
charm has a mass of 1200 MeV.
tau has a mass of 1776.86 MeV.

The code now works. We see that the program prints out the number of particles in the list and the order of the particles by ascending mass in MeV.

Example #2: Not Including a Return Statement

We can put the sorting steps in the previous example in its function. We can use the same particle list and sorting function as follows:

particles = [
 {"name":"electron", "mass": 0.511},
 {"name":"muon", "mass": 105.66},
 {"name":"tau", "mass": 1776.86},
 {"name":"charm", "mass":1200},
 {"name":"strange", "mass":120}
]
def particle_sort(p):
    return p["mass"]

The next step involves writing a function that sorts the list using the “mass” as the sorting key.

def sort_particles_list(particles):
    particles.sort(key=particle_sort)

Then we can define a function that prints out the number of particles in the list and the ordered particles by ascending mass:

def show_particles(sorted_particles):
    print("There are {} particles in the list.".format(len(sorted_particles)))
    for p in sorted_particles:
    
        print("{} has a mass of {} MeV.".format(p["name"],p["mass"]))

Our program needs to call the sort_particles_list() function and the show_particles() function.

sorted_particles = sort_particles_list(particles)
show_particles(sorted_particles)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-64-65566998d04a> in <module>
----> 1 show_particles(sorted_particles)
<ipython-input-62-6730bb50a05a> in show_particles(sorted_particles)
      1 def show_particles(sorted_particles):
----> 2     print("There are {} particles in the list.".format(len(sorted_particles)))
      3     for p in sorted_particles:
      4         print("{} has a mass of {} MeV.".format(p["name"],p["mass"]))
      5 
TypeError: object of type 'NoneType' has no len()

The error occurs because we did not include a return statement in the sort_particles_list() function. We assign the sort_particles_list() output to the variable sorted_particles, then pass the variable to show_particles() to get the information inside the list.

Solution

We need to add a return statement to the sort_particles_list() function to solve the error.

def sort_particles_list(particles):
    particles.sort(key=particle_sort)
    return particles
sorted_particles = sort_particles_list(particles)
show_particles(sorted_particles)

There are 5 particles in the list.
electron has a mass of 0.511 MeV.
muon has a mass of 105.66 MeV.
strange has a mass of 120 MeV.
charm has a mass of 1200 MeV.
tau has a mass of 1776.86 MeV.

Summary

Congratulations on reading to the end of this tutorial!

For further reading on the len() method, go to the article: How to Find the Length of a List in Python.

For further reading on the has no len() TypeErrors, go to the article:

How to Solve Python TypeError: object of type ‘function’ has no len()

To learn more about Python for data science and machine learning, go to the online courses page on Python, which provides the best, easy-to-use online courses.

The TypeError: object of type ‘NoneType’ has no len() error occurs while attempting to find the length of an object that returns ‘None’. The python object whose data type is NoneType can’t be used in length function. The Length function is used for data structures that store multiple objects.

The python variables, which have no value initialised, have no data type. These variables are not assigned any value, or objects. The length function can not be called the variables which are not allocated with any value or object. If you call the length function for these variables of none type, it will throw the error TypeError: object of type ‘NoneType’ has no len()

Exception

The error TypeError: object of type ‘NoneType’ has no len() will display the stack trace as below

Traceback (most recent call last):
  File "/Users/python/Desktop/test.py", line 2, in <module>
    print (len(s))
TypeError: object of type 'NoneType' has no len()
[Finished in 0.1s with exit code 1]

How to reproduce this error

If a python variable is not assigned with any value, or objects, the variable would have none data type. If the length function is invoked for the none type variable, the error TypeError: object of type ‘NoneType’ has no len() will be thrown.

test.py

s=None
print (len(s))

Output

Traceback (most recent call last):
  File "/Users/python/Desktop/test.py", line 2, in <module>
    print (len(s))
TypeError: object of type 'NoneType' has no len()
[Finished in 0.1s with exit code 1]

Solution 1

The python variable which is not assigned with any value or object, should be assigned with a value or object. If the variable is not assigned with any value or object , assign with an object such as list, tuple, set, dictionary etc.

s=[1,2]
print (len(s))

Output

2
[Finished in 0.0s]

Solution 2

Due to the dynamic creation of the variable the python variable may not be assigned with values. The datatype of the variable is unknown. In this case, the None data type must be checked before the length function is called.

s=None
print type(s)
if s is None : 
	print "Value is None"
else:
	print (len(s))

Output

Value is None

Solution 3

The python variable should be validated for the expected data type. If the variable has the expected data type, then the length function should be invoked. Otherwise, the alternate flow will be invoked.

s=None
print type(s)
if type(s) in (list,tuple,dict, str): 
	print (len(s))
else:
	print "not a list"

Output

not a list

Solution 4

If the data type of the variable is unknown, the length function will be invoked with try and except block. The try block will execute if the python variable contains value or object. Otherwise, the except block will handle the error.

s=None
try :
	print (len(s))
except :
	print "Not a list"

Output

Not a list
[Finished in 0.0s]

When working with Python, you will likely encounter the error “TypeError: object of type ‘NoneType’ has no len()”. Let’s learn about the cause of this error as well as its solution through this article. Keep reading for detailed information.

What causes this error?

You will get the error message: “TypeError: object of type ‘NoneType’ has no len()” in Python when you try to pass in the len() function a value ‘None’.

The len() function in Python takes a single parameter – a collection or a sequence – and returns the length of that object.

Syntax:

len(object)

Where: object – Required parameter. An object. It must be a collection or a sequence.

Therefore, if you pass in the len() function a value of ‘None’, the error is obvious.

Here is an example of how this error occurs:

def getMessage():
    print("Welcome to the LearnShareIT community.")

# None value
message = getMessage()
print(len(message))

Error:

TypeError: object of type 'NoneType' has no len()

Since the getMessage() function does not return any value, the ‘message’ variable gets a value of ‘None’.

To work around this problem, ensure that the value you pass to len() is different from ‘None’.

As in the above example, we can use the return statement to get a value from the function.

def getMessage():
    return "Welcome to the LearnShareIT community."

message = getMessage()
print(len(message))

Output:

38

Alternatively, you can also use the conditional statement to check if a variable is storing a ‘None’ value before passing it into the len() function.

message = None

# Use the if/else block
if message != None:
    print(len(message))
else:
    print("The variable is storing a 'None' value")

Output:

The variable is storing a 'None' value

At this point, you no longer have to worry about the error because the conditional statement prevents getting the length of a variable that stores a ‘None’ value. 

Or you can also directly print the variable to be checked to see its value with the print() statement.

noneMessage = None
message = "Welcome to the LearnShareIT community."

print(noneMessage)
print(message)

Output:

None
Welcome to the LearnShareIT community.

Summary

In summary, we have just shared with you the necessary information about the “TypeError: object of type ‘NoneType’ has no len()” in Python. To overcome this error, you need to check the value of the variable passed in the len() function and make sure it is different from a ‘None’ value. That’s the end of this post. Hopefully, the information we conveyed will be helpful to you.