Question

I read this and got really interested: Validating date format using regular expression

so I started writing my own version of the date validation function, I think I am close, but not quite, and I would like some suggestion as well as tips. I have spend a lot of time trying to tweak the function.

import re
import datetime

# Return True if the date is in the correct format
def checkDateFormat(myString):
    isDate = re.match('[0-1][0-9]\/[0-3][0-9]\/[1-2][0-9]{3}', myString)
    return isDate

# Return True if the date is real date, by real date it means,
# The date can not be 00/00/(greater than today)
# The date has to be real (13/32) is not acceptable
def checkValidDate(myString):
    # Get today's date
    today = datetime.date.today()
    myMaxYear = int(today.strftime('%Y'))

    if (myString[:2] == '00' or myString[3:5] == '00'):
        return False

    # Check if the month is between 1-12
    if (int(myString[:2]) >= 1 or int(myString[:2]) <=12):
        # Check if the day is between 1-31
        if (int(myString[3:5]) >= 1 or int(myString[3:2]) <= 31):
            # Check if the year is between 1900 to current year
            if (int(myString[-4:]) <= myMaxYear):
                return True
    else:
        return False

testString = input('Enter your date of birth in 00/00/0000 format: ')

# Making sure the values are correct
print('Month:', testString[:2])
print('Date:', testString[3:5])
print('Year:', testString[-4:])

if (checkDateFormat(testString)):
    print('Passed the format test')
    if (checkValidDate(testString)):
        print('Passed the value test too.')
    else:
        print('But you failed the value test.')
else:
    print("Failed. Try again")

Question 1: Is there other way (better) to do int(myString[3:5]) when I want to compare if it is valid? I feel my method is very repetitive, and this function must require 00/00/0000, otherwise it will break. So the function isn’t all that useful in that sense. Especially the way I handle my 00/01/1989, it is just simply comparing if they are indeed 00.

Question 2: There are many if statement, I wonder are there better way to write this test?

I would like to learn more about programming in python, any suggestion or advice will be greatly appreciated. Thank you very much.

Answer 1

Like many things in python there’s already underlying capabilities to check dates. Assuming you aren’t just doing this as an academic exercise the most straightforward way to validate a date is to try and create it.

import datetime

minyear = 1900
maxyear = datetime.date.today().year

mydate = '12/12/2000'
dateparts = mydate.split('/')
try:
    if len(dateparts) != 3:
       raise ValueError("Invalid date format")
    if int(dateparts[2]) > maxyear or int(dateparts[2]) < minyear:
       raise ValueError("Year out of range")
    dateobj = datetime.date(int(dateparts[2]),int(dateparts[1]),int(dateparts[0]))
except:
    // handle errors

if datetime.date is given an invalid date it will complain, eg:

datetime.date(2000,45,23)

Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    datetime.date(2000,45,23)
ValueError: month must be in 1..12