How to Validate a Date String Format in Python

How do I validate a date string format in python?

>>> import datetime
>>> def validate(date_text):
        try:
            datetime.datetime.strptime(date_text, '%Y-%m-%d')
        except ValueError:
            raise ValueError("Incorrect data format, should be YYYY-MM-DD")

    
>>> validate('2003-12-23')
>>> validate('2003-12-32')

Traceback (most recent call last):
  File "<pyshell#20>", line 1, in <module>
    validate('2003-12-32')
  File "<pyshell#18>", line 5, in validate
    raise ValueError("Incorrect data format, should be YYYY-MM-DD")
ValueError: Incorrect data format, should be YYYY-MM-DD

Check if string has date, any format

The parse function in dateutils.parser is capable of parsing many date string formats to a datetime object.

If you simply want to know whether a particular string could represent or contain a valid date, you could try the following simple function:

from dateutil.parser import parse

def is_date(string, fuzzy=False):
    """
    Return whether the string can be interpreted as a date.

    :param string: str, string to check for date
    :param fuzzy: bool, ignore unknown tokens in string if True
    """
    try: 
        parse(string, fuzzy=fuzzy)
        return True

    except ValueError:
        return False

Then you have:

>>> is_date("1990-12-1")
True
>>> is_date("2005/3")
True
>>> is_date("Jan 19, 1990")
True
>>> is_date("today is 2019-03-27")
False
>>> is_date("today is 2019-03-27", fuzzy=True)
True
>>> is_date("Monday at 12:01am")
True
>>> is_date("xyz_not_a_date")
False
>>> is_date("yesterday")
False

Custom parsing

parse might recognise some strings as dates which you don't want to treat as dates. For example:

• Parsing "12" and "1999" will return a datetime object representing the current date with the day and year substituted for the number in the string

• "23, 4" and "23 4" will be parsed as datetime.datetime(2023, 4, 16, 0, 0).

• "Friday" will return the date of the nearest Friday in the future.
• Similarly "August" corresponds to the current date with the month changed to August.

Also parse is not locale aware, so does not recognise months or days of the week in languages other than English.

Both of these issues can be addressed to some extent by using a custom parserinfo class, which defines how month and day names are recognised:

from dateutil.parser import parserinfo

class CustomParserInfo(parserinfo):

    # three months in Spanish for illustration
    MONTHS = [("Enero", "Enero"), ("Feb", "Febrero"), ("Marzo", "Marzo")]

An instance of this class can then be used with parse:

>>> parse("Enero 1990")
# ValueError: Unknown string format
>>> parse("Enero 1990", parserinfo=CustomParserInfo())
datetime.datetime(1990, 1, 27, 0, 0)

how to validate a date in python

Rather than use time.strptime(), use datetime.datetime.strptime() and then validate the resulting object to be within your range:

from datetime import datetime, date
date_input = input('Date (mm/dd/yyyy): ')
try:
    valid_date = datetime.strptime(date_input, '%m/%d/%Y').date()
    if not (date(2014, 1, 1) <= valid_date <= date(2014, 8, 7)):
        raise ValueError('Date out of range')
except ValueError:
    print('Invalid date!')

If no exception is thrown, valid_date is bound to a datetime.date() instance.

How to validate a string input in python using datetime library and keep prompting user for input until valid input?

This code works on my machine, and it prompts the user to input again if it doesn't succeed.

import datetime
format = "%Y-%m-%d"

while(True):
    date_string = input("> ").strip()
    try:
        datetime.datetime.strptime(date_string, format)
        print("This is the correct date string format.")
        break
    except ValueError:
        print("This is the incorrect date string format. It should be YYYY-MM-DD")

validate date format in python [with regex or any built in method]

you can use datetime for this (in python 2.7)

from datetime import datetime

date_string = '20170808'

if len(date_string) == 8:
   datetime.strptime(date_string, '%Y%m%d')
else:
   raise ValueError('date need to be in format YYYYMMDD ')

if you date is not valid than you get:

a ValueError Exception

ValueError: unconverted data remains: 0

Checking if date is valid with two different format

Simply do try for each datetime.strptime and catch each error seperatly.

def dateValidate(date):
    try:
        datetime.strptime(date, "%Y-%m-%d")
        return 1
    except ValueError:
        try:
            datetime.strptime(date, "%m/%d/%Y")
            return 2
        except ValueError:
            return -1

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