If someone inserts a string '2021-11-31' that doesn't exist as a date. How to correct the date like '2021-11-30'(last day of month) or '2021-12-01'(first day) with python?

The input date can be '2021-02-34' or '2021-12-35' or many wrong input.. and I want to make it a last day of month or a first day of next month.

The point is

1. The program should know that the date is wrong or correct
2. and then correct the date

Thank you!

CodePudding user response：

As mentioned by Yunnosch in previous comments, you can't be sure the date is "correct".

I guess you're assuming the date format to be YYYY-MM-DD and want to constrain DD to be within 1-31 (or 1-28, 1-29, 1-30 depending on the month).

Here is a simple function that does this :

import calendar


def rectify_day(dt: str) -> str:
    """
    Rectify the date and month of a date.
    If the day part is greater than the last day of this month,
    it will constrain the day to be the last day of month.
    """
    year_s, month_s, day_s = dt.split("-")   # split the elements of the date
    year = int(year_s)                       # convert them to integers
    month = int(month_s)
    day = int(day_s)
    last_day_of_month = calendar.monthrange(year, month)[1] # get the last day of this month
    day = min(day, last_day_of_month)        # constrain the day to max possible value

    return f"{year}-{month:>02d}-{day:>02d}" # returns a formatted string

Use it like that :

>>> rectify_day("2021-01-32")
'2021-01-31'
>>> rectify_day("2021-02-29")
'2021-02-28'
>>> rectify_day("2021-01-10")
'2021-01-10'
>>> rectify_day("2021-12-12")
'2021-12-12'