While loop is starting even when parameters aren't met

Question

I've been trying to run this Python code:

type = input("Please enter the file type ('video' or 'audio'): ")

while type != "video" or type != "audio":
    type = input("Please enter a valid format ('video' or 'audio'): ")
    if type == "video" or type == "audio":
        break

The problem: Even when the conditions aren't met (e.g: the format is 'video') the while loop begins, you can break out of it by simply typing the required format again, but it's very inconvenient, any help?

type would be "audio" or "video" so your statement will always be true cause if `type!="video"` is `False` (means that type is "video") then `type!="audio"` will be `True` ... so your condition will be always `True` — Ulises Bussi, Nov 04 '21 at 20:32
BTW, welcome to Stack Overflow! Check out the [tour], and [ask] if you want tips. — wjandrea, Nov 04 '21 at 20:37
Related: [Asking the user for input until they give a valid response](/q/23294658/4518341) — wjandrea, Nov 04 '21 at 20:39

score 2 · Accepted Answer · edited Nov 04 '21 at 20:43

2

I think the correct code is:

t = ""

while t not in ["video", "audio"]:
    t = input("Please enter a valid format ('video' or 'audio'): ")

edited Nov 04 '21 at 20:43

Sylvester Kruin

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answered Nov 04 '21 at 20:32

Adrian B

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score 2 · Answer 2 · answered Nov 04 '21 at 20:36

while type != "video" or type != "audio"

That while condition will ALWAYS be true.

If they entered "video", then the != "audio" part will be true.

If they entered "audio", then the != "video" part will be true.

If they entered anything else, then both parts will be true.

Use and instead of or:

while type != "video" and type != "audio"

Or, even better, check for membership in a list:

while type not in ["video", "audio"]:

And better still, don't use built-in names such as type for your variables.

Corralien · Answer 3 · 2021-11-04T20:36:59.530

1

Change or by and:

# HERE -------------v
while t != "video" and t != "audio":
    print(t)
    t = input("Please enter a valid format ('video' or 'audio'): ")

edited Nov 04 '21 at 20:36

answered Nov 04 '21 at 20:34

Corralien

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score 0 · Answer 4 · answered Nov 04 '21 at 20:36

0

NOT x OR NOT y is not the opposite of x OR y, that's NOT (x OR y). Or, using De Morgan's laws, NOT x AND NOT y.

That said, using not in is much simpler. See Adrian B's answer.

answered Nov 04 '21 at 20:36

wjandrea

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flakes · Answer 5 · 2021-11-04T20:48:53.033

I would put this logic in its own function to avoid complicated loop structures and make the code more readable. I would do something like this:

def get_media_type_input():
    while True:
        media_type = input("Please enter a valid format ('video' or 'audio'): ")
        if media_type in ("video", "audio"):
            return media_type
        else:
            print(f"Invalid media type {media_type}. Try again")

...

media_type = get_media_type_input()

You could then extend this to make the method more generic:

def get_format_type_input(title, choices):
    while True:
        choice = input(
            f"Please enter a valid {title} format "
            f"({', '.join(choices)}): "
        )
        if choice in choices:
            return choice
        else:
            print(f"Invalid {title} format '{choice}'. Try again.")


media_type = get_format_type_input("media", ["video", "audio"])

While loop is starting even when parameters aren't met

5 Answers5