如何为包含两个日期的输入引发可自定义的 ValueError？

Question

I am trying to understand raising an exception little better.Below is python code, as you can see I am asking for two date inputs from user. If user types "2022" and hit enter it is returning python ValueError with msg "Not enough values to unpack (expected 2, got 1)" . Instead what I would like to do is if user types year,month or date then instead of python default ValueError. It should raise an Error saying "Incorrect date entered, please enter dates in YYYY-MM-DD format ONLY" and should display the input box again for user to enter correct date. My question is how to raise customizable ValueError and ask the user to renter the dates?

Any help will be appreciated!

Code

def validate(date_text):
        try:
            for y in date_text:
                if not datetime.datetime.strptime(date_text, '%Y-%m-%d'):
                    raise ValueError
                else:
                    return True
        except ValueError:
            print("Incorrect date format, please enter dates in YYYY-MM-DD format ONLY")
            return False
while True:
    start_date,end_date= input("Enter employee start and termination date separated by (,)  in YYYY-MM-DD format only: ").split(",")
    if validate(start_date) and validate(end_date):
        break

Answer 1

You get ValueError: not enough values to unpack (expected 2, got 1) because your are setting 2 variables to input('...').split(',') . They expect a string consisting of 2 parts, divided by a comma. For example if you input a string with more than one comma, you will get too many values to unpack .

Its got to be like this:

Enter two values divided by a comma:1,2

Then, i find that your first raise ValueError statement is not necessary. If the argument to datetime.datetime.strptime is incorrect it won't go to that raise anyway.

I would dispose of it, along with the if block:

import datetime
def validate(date_text):
        try:
            datetime.datetime.strptime(date_text, '%Y-%m-%d')
            return True
        except ValueError:
            print("Incorrect date format, please enter dates in YYYY-MM-DD format ONLY")
            return False
while True:
    start_date,end_date= input("Enter employee start and termination date separated by (,)  in YYYY-MM-DD format only: ").split(",")
    if validate(start_date) and validate(end_date):
        break

Answer 2

I was able to resolve my issue using below code. Basically, I needed another try & except block in while statement. Thanks @Иван Балван for feedback!

def validate(date_text):
        try:
            datetime.datetime.strptime(date_text, '%Y-%m-%d')
            return True
        except ValueError:
            print("Incorrect date format, please enter dates in YYYY-MM-DD format ONLY")
            return False

while True:
    try:
        start_date,end_date= input("Enter employee start and termination date separated by (,)  in YYYY-MM-DD format only: ").split(",")
        if validate(start_date) and validate(end_date):
            break
    except ValueError:
        print("Incorrect date enetered, please enter both dates in YYYY-MM-DD format ONLY")