Validating date format with Python regex

Question

I want to check if the format of the date input by user matches the below:

Jan 5 2018 6:10 PM

Month: First letter should be caps, followed 2 more in small. (total 3 letters)
<Space>: single space, must exist
Date: For single digit it should not be 05, but 5
<Space>: single space, must exist
Hour: 0-12, for single digit it should not be 06, but 6
Minute: 00-59
AM/PM

I'm using the below regex and trying to match:

import re,sys
usr_date = str(input("Please enter the older date until which you want to scan ? \n[Date Format Example: Jan 5 2018 6:10 PM] :  "))

valid_usr_date = re.search("^(\s+)*[A-Z]{1}[a-z]{2}\s{1}[1-31]{1}\s{1}[1-2]{1}[0-9]{1}[0-9]{1}[0-9]{1}\s{1}[0-12]{1}:[0-5]{1}[0-9]{1}\s{1}(A|P)M$",usr_date,re.M)

if not valid_usr_date:
    print ("The date format is incorrect. Please follow the exact date format as shown in example. Exiting Program!")
    sys.exit()

But, even for the correct format it gives a syntax wrong error. What am I doing wrong.

[1-31] matches 1, 2 or 3. Character classes do not work as you think they do. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jan 30, 2018 at 8:18
@WiktorStribiżew you have the right answer, but you entered it as a "comment". Write it as an "answer" instead, and the questioner can give you credit for your answer! — Jim DeLaHunt
– Jim DeLaHunt, Commented Jan 30, 2018 at 8:19
Can I ask why use this format and not something that can be easily parsed by datetime.strptime? — Reut Sharabani
– Reut Sharabani, Commented Jan 30, 2018 at 8:31
@ReutSharabani This code above is part of a bigger code with a lot of functions defined. I already have certain functions where I'm parsing different parts of the date with datetime.strptime, but that is well ahead in my program. Before even going there I want to keep a validate function where I validate all inputs from user, and if doesn't validate, the program exits and doesn't go any further. Moreover I don't want to bind my program modules with multiple try: except:. I, rather am using sys.excepthook which captures all exceptions — dig_123
– dig_123, Commented Jan 30, 2018 at 9:09

DeepSpace · Accepted Answer · 2018-01-30 08:44:46Z

8

I would not use regex for that, as you have no way to actually validate the date itself (eg, a regex will happily accept Abc 99 9876 9:99 PM).

Instead, use strptime:

from datetime import datetime

string = 'Jan 5 2018 6:10 PM'
datetime.strptime(string, '%b %d %Y %I:%M %p')

If the string would be in the "wrong" format you'd get a ValueError.

The only apparent "problem" with this approach is that for some reason you require the day and hour not to be zero-padded and strptime doesn't seem to have such directives.

A table with all available directives is here.

edited Jan 30, 2018 at 8:44

answered Jan 30, 2018 at 8:22

DeepSpace

82.1k12 gold badges119 silver badges166 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

AnythingIsFine · Accepted Answer · 2018-01-30 08:24:17Z

1

You could use a function which parses the input string and tries to return a datetime object, if it can't it raises an ValueError:

from datetime import datetime

def valid_date(s):
    try:
        return datetime.strptime(s, '%Y-%m-%d %H:%M')
    except ValueError:
        msg = "Not a valid date: '{0}'.".format(s)
        raise argparse.ArgumentTypeError(msg)

answered Jan 30, 2018 at 8:24

AnythingIsFine

1,81516 silver badges11 bronze badges

1 Comment

dig_123 Over a year ago

This code I mentioned above in my query, is part of a bigger code with a lot of functions defined. I already have certain functions where I'm parsing different parts of the date with datetime.strptime, but that is well ahead in my program. Before even going there I want to keep a validate function where I validate all inputs from user, and if doesn't validate, the program exits and doesn't go any further. Moreover I don't want to bind my program modules with multiple try: except:. I, rather am using sys.excepthook which captures all exceptions

Collectives™ on Stack Overflow

Validating date format with Python regex

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related