Trying to exit While True loop but it won't

Question

I wanted it to print out the date and stop but it would keep printing "Enter: " even though there is "break" and it printed out the date successfully.

while True:
    user = input("Enter: ")
    if "/" not in user:
        if "," in user:
            date = user.replace(",", "")
        date = date.split(" ")
        date = list(date)
        for i in range(len(date)):
            if date[i] in month:
                mnth = month[f"{date[i]}"]
                if int(date[1]) < 10:
                    date[1] = "0" + date[1]
                print(f"{date[2]}-{mnth}-{date[1]}")
                break

You can only beak out of the innermost loop. So that breaks out of the `for` loop, not the `while` loop. — Barmar, Jul 23 '22 at 17:07
If you want `break` to break out of the `while True` loop, you need to align it the same as `user = input("Enter: ")`. — MattDMo, Jul 23 '22 at 17:07
`date = list(date)` is unnecessary. `split()` returns a list. — Barmar, Jul 23 '22 at 17:09
Why are you looping over `date`, but then using hard-coded indexes inside the loop? What exactly is this code trying to do? — Barmar, Jul 23 '22 at 17:10
It prints dates as year-month-date format. It loops over date so that it checks if there is a month in it and checks if that month is in a dictionary. Thanks — Eric Lee, Jul 23 '22 at 17:14

score 0 · Answer 1 · answered Jul 23 '22 at 17:11

Since you can only break out of the innermost loop directly, you need to use a variable to tell the outer loop to stop.

done = False
while not done:
    user = input("Enter: ")
    if "/" not in user:
        date = user.replace(",", "")
        date = date.split(" ")
        for i in range(len(date)):
            if date[i] in month:
                mnth = month[f"{date[i]}"]
                if int(date[1]) < 10:
                    date[1] = "0" + date[1]
                print(f"{date[2]}-{mnth}-{date[1]}")
                done = True
                break

I also got rid of the unneeded date = list(date).

The if "," in user: check shouldn't be done, because you never set date if there's no , to replace. Just call replace() and if there aren't any , it will return the string unchanged.

Samwise · Answer 2 · 2022-07-23T18:27:07.487

One way to break an outer loop from an inner loop without adding an extra variable to keep track of is to use else: continue followed by a break:

while True:
    user = input("Enter: ")
    if "/" not in user:
        if "," in user:
            date = user.replace(",", "")
        date = date.split(" ")
        date = list(date)
        for i in range(len(date)):
            if date[i] in month:
                mnth = month[f"{date[i]}"]
                if int(date[1]) < 10:
                    date[1] = "0" + date[1]
                print(f"{date[2]}-{mnth}-{date[1]}")
                break
        else:
            continue  # continue if the for loop wasn't broken
        break         # break the while if we didn't continue

As explained in the comments, the trick is that the else of the for executes if there was no break -- we can therefore continue the while if and only if there was no break inside the for, and explicitly break the while otherwise.

Not directly related to that, I'd suggest battling some of that indentation by using continue elsewhere in the loop, and getting rid of all the unnecessary string manipulation (note the use of {date[1]:0>2} to zero-pad to two digits without needing the int math -- neat, eh?):

while True:
    user = input("Enter: ")
    if "/" in user:
        continue
    date = user.replace(",", "").split(" ")
    for mm in date:
        if mm not in month:
            continue
        print(f"{date[2]}-{mm}-{date[1]:0>2}")
        break
    else:
        continue
    break

and since your code seems to assume that date[2] is always the year and date[1] is always the day of the month, I'm going to go out on a limb and guess that you can also safely assume the month is always date[0] if it's anything at all, which means you can skip that whole inner loop and just do:

while True:
    user = input("Enter: ")
    if "/" in user:
        continue
    mm, dd, yyyy = user.replace(",", "").split(" ")[:3]
    if mm not in month:
        continue
    print(f"{yyyy}-{mm}-{dd:0>2}")
    break

Trying to exit While True loop but it won't

2 Answers2