Using try after except is not working on Python

Question

I’m doing exercise 4 on CS50P "outdated" and after trying to make the code work with if/else statements I came across a solution that used try/except for dealing with cases instead of if/else. In the following code I don’t understand why the second except gets executed and thus, renders the second part of the code useless.

months = [
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December"
]

while True:
    msg = input("Date: ")
    try:
        msg = msg.split("/")
        msg[0] = int(msg[0])
        msg[1] = int(msg[1])
        msg[2] = int(msg[2])
        if 0 < msg[0] < 13 and 0 < msg[1] < 32 and 0 < msg[2]:
            MM = f"{msg[0]:02}"
            DD = f"{msg[1]:02}"
            YY = f"{msg[2]:02}"
            break
    except:
        try:
            msg = msg.split(" ")
            msg[0] = int(months.index(msg[0])+1)
            msg[1] = msg[1].replace(",","")
            msg[1] = int(msg[1])
            msg[2] = int(msg[2])
            if 0 < msg[0] < 13 and 0 < msg[1] < 32 and 0 < msg[2]:
                MM = f"{msg[0]:02}"
                DD = f"{msg[1]:02}"
                YY = f"{msg[2]:02}"
                break
        except:

            print()
            pass

print(YY,MM,DD, sep="-")

When I try to execute the msg.split(" ") part first, it does work and then the following part doesn’t work. Right now I have only been able to execute the first part (the code before the except). I would like to know where is the error since the terminal does not show any.

Asked By: Angel Trejo

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Source

Answer 1

Rather than a linear approach to this problem you should write two discrete functions for handling the two possible input date formats.

The allowed formats are:

MM/DD/YYYY
MM DD, YYYY

In the second format MM is a month full name – e.g., September

Use the datetime module to try to construct a datetime object from the user input. Anything invalid in the user input will cause an exception to be raised during construction of the datetime object.

from calendar import month_name
from datetime import datetime

# Possibly MM/DD/YYYY format
def type_1(s):
    if len(parts := s.split('/')) == 3:
        mm, dd, yyyy = map(int, parts)
        return datetime(yyyy, mm, dd)


# Possibly MM DD, YYYY where MM is months fullname - e.g., September
def type_2(s):
    if len(parts := s.replace(',', '').split()) == 3:
        mm = [*month_name].index(parts[0])
        dd, yyyy = map(int, parts[1:])
        return datetime(yyyy, mm, dd)


while user_date := input('Enter a date: '):
    for func in type_1, type_2:
        try:
            if d := func(user_date):
                print(datetime.strftime(d, '%Y-%m-%d'))
                break
        except Exception:
            pass
    else:
        print('Invalid date')

Answered By: Fred

Using try after except is not working on Python

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