Как найти дату в строке python

Instead of using regex, it is generally better to parse the string as a datetime.datetime object:

In [140]: datetime.datetime.strptime("11/12/98","%m/%d/%y")
Out[140]: datetime.datetime(1998, 11, 12, 0, 0)

In [141]: datetime.datetime.strptime("11/12/98","%d/%m/%y")
Out[141]: datetime.datetime(1998, 12, 11, 0, 0)

You could then access the day, month, and year (and hour, minutes, and seconds) as attributes of the datetime.datetime object:

In [143]: date.year
Out[143]: 1998

In [144]: date.month
Out[144]: 11

In [145]: date.day
Out[145]: 12

To test if a sequence of digits separated by forward-slashes represents a valid date, you could use a try..except block. Invalid dates will raise a ValueError:

In [159]: try:
   .....:     datetime.datetime.strptime("99/99/99","%m/%d/%y")
   .....: except ValueError as err:
   .....:     print(err)
   .....:     
   .....:     
time data '99/99/99' does not match format '%m/%d/%y'

If you need to search a longer string for a date,
you could use regex to search for digits separated by forward-slashes:

In [146]: import re
In [152]: match = re.search(r'(d+/d+/d+)','The date is 11/12/98')

In [153]: match.group(1)
Out[153]: '11/12/98'

Of course, invalid dates will also match:

In [154]: match = re.search(r'(d+/d+/d+)','The date is 99/99/99')

In [155]: match.group(1)
Out[155]: '99/99/99'

To check that match.group(1) returns a valid date string, you could then parsing it using datetime.datetime.strptime as shown above.

You can run a date parser on all subtexts of your text and pick the first date. Of course, such solution would either catch things that are not dates or would not catch things that are, or most likely both.

Let me provide an example that uses dateutil.parser to catch anything that looks like a date:

import dateutil.parser
from itertools import chain
import re

# Add more strings that confuse the parser in the list
UNINTERESTING = set(chain(dateutil.parser.parserinfo.JUMP, 
                          dateutil.parser.parserinfo.PERTAIN,
                          ['a']))

def _get_date(tokens):
    for end in xrange(len(tokens), 0, -1):
        region = tokens[:end]
        if all(token.isspace() or token in UNINTERESTING
               for token in region):
            continue
        text = ''.join(region)
        try:
            date = dateutil.parser.parse(text)
            return end, date
        except ValueError:
            pass

def find_dates(text, max_tokens=50, allow_overlapping=False):
    tokens = filter(None, re.split(r'(S+|W+)', text))
    skip_dates_ending_before = 0
    for start in xrange(len(tokens)):
        region = tokens[start:start + max_tokens]
        result = _get_date(region)
        if result is not None:
            end, date = result
            if allow_overlapping or end > skip_dates_ending_before:
                skip_dates_ending_before = end
                yield date


test = """Adelaide was born in Finchley, North London on 12 May 1999. She was a 
child during the Daleks' abduction and invasion of Earth in 2009. 
On 1st July 2058, Bowie Base One became the first Human colony on Mars. It 
was commanded by Captain Adelaide Brooke, and initially seemed to prove that 
it was possible for Humans to live long term on Mars."""

print "With no overlapping:"
for date in find_dates(test, allow_overlapping=False):
    print date


print "With overlapping:"
for date in find_dates(test, allow_overlapping=True):
    print date

The result from the code is, quite unsurprisingly, rubbish whether you allow overlapping or not. If overlapping is allowed, you get a lot of dates that are nowhere to be seen, and if if it is not allowed, you miss the important date in the text.

With no overlapping:
1999-05-12 00:00:00
2009-07-01 20:58:00
With overlapping:
1999-05-12 00:00:00
1999-05-12 00:00:00
1999-05-12 00:00:00
1999-05-12 00:00:00
1999-05-03 00:00:00
1999-05-03 00:00:00
1999-07-03 00:00:00
1999-07-03 00:00:00
2009-07-01 20:58:00
2009-07-01 20:58:00
2058-07-01 00:00:00
2058-07-01 00:00:00
2058-07-01 00:00:00
2058-07-01 00:00:00
2058-07-03 00:00:00
2058-07-03 00:00:00
2058-07-03 00:00:00
2058-07-03 00:00:00

Essentially, if overlapping is allowed:

1. “12 May 1999” is parsed to 1999-05-12 00:00:00
2. “May 1999” is parsed to 1999-05-03 00:00:00 (because today is the 3rd day of the month)

If, however, overlapping is not allowed, “2009. On 1st July 2058” is parsed as 2009-07-01 20:58:00 and no attempt is made to parse the date after the period.

Given a date format and a string date, the task is to write a python program to check if the date is valid and matches the format.

Examples:

Input : test_str = ’04-01-1997′, format = “%d-%m-%Y”

Output : True

Explanation : Formats match with date.

Input : test_str = ’04-14-1997′, format = “%d-%m-%Y”

Output : False

Explanation : Month cannot be 14.

Method #1 : Using strptime()

In this, the function, strptime usually used for conversion of string date to datetime object, is used as when it doesn’t match the format or date, raises the ValueError, and hence can be used to compute for validity.

Output:

The original string is : 04-01-1997
Does date match format? : True

Method #2 : Using dateutil.parser.parse()

In this, we check for validated format using different inbuilt function, dateutil.parser. This doesn’t need the format to detect for a date.

Output:

The original string is : 04-01-1997
Does date match format? : True

Method#3: Using regular expression

Approach

validate a string date format is by using regular expressions. We can define a regular expression pattern that matches the expected format, and then use the re module to check if the string matches the pattern.

Algorithm

1. Import the re module
2. Define the input test string and the regular expression pattern string
3. Use the re.match() method to match the pattern against the test string
4. If the pattern matches the test string:
a. Print “True”
5. Otherwise:
a. Print “False”

Time complexity of this approach is O(n), where n is the length of the input string. 

Auxiliary Space is also O(n), since we need to store the regular expression pattern in memory.

Last Updated :
14 Mar, 2023

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