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in python, how do i check if an user boolean input is true or false (lemmy.ml)

submitted 1 year ago by jackpot@lemmy.ml to c/asklemmy@lemmy.ml

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to my knowledge, if you input any text it will return true and if you input nothing it will return false. if it's possible without if statements, how do i check if they inputted 'True' or 'False (/ '1' or '0') when im doing 'bool(input("Input True or False ")'.

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[–] Blake@feddit.uk 5 points 1 year ago

Text input by a user is almost always a string, because the user presses 0 or more keys on their keyboard before hitting enter.

Without validation, we have no way to know that the user typed - did they type “1” or “True”, or did they embrace chaos and type in “Batman”? Unless we check, we can’t be sure.

We can assume, but then we have to accept that our program will have what we call “undefined behaviour” if our assumption is incorrect - which is definitely not good. In the best case scenario, your code harmlessly crashes. In the worst case scenario, your code is being used by the Pentagon for some reason and just started global thermonuclear war, which ideally should be avoided.

There are ways around this. For example, we could listen for individual keystrokes and only accept the inputs if they meet our criteria - if the user presses the 1 key, that’s true, if they press 0, that’s false, any other key is ignored, for example.

But the best thing to do, in my humble opinion, is to accept a string input and then check what the user entered. In most cases, “True” or “False” aren’t usually what we want, unless you’re writing some sort of true or false guessing game or something. Most cases where we want a Boolean input from a user, it’s a yes/no kind of thing. “Would you like to continue?” or “Shall we start global thermonuclear war? y/N”

So you’re better off just embracing the string, and using that to determine behaviour, rather than a Boolean directly. For example, something along the lines of :

if user input is “y” then launch nukes
else if user input is “n” send fruit basket
else print “input invalid”`

As others mentioned in the thread, it may be wise to convert the input to lowercase - just in case the user enters Y or y. Personally I wouldn’t go so far as to take the first letter as the answer, in case the user enters “you must be joking!” for example :-)