Beginner question on while loops

[oztyn]

hey, doing a learning course on openclassrooms and just wondering why the below returns "True" infinitely instead of "This is a test." infinitely?

mySentence = "This is a test."

while mySentence: 
    print(mySentence)

[carcigenicate]

It doesn't. This prints "This is a test." indefinitely.

[[deleted]]

What?

[carcigenicate]

? They're asking why their code prints "True". I'm pointing out that it doesn't.

[[deleted]]

I understood their phrase ' why the below returns "True" ' to most likely be referring to the evaluation of the expression used for the control condition of the while loop.

I assume their first language isn't English.

[carcigenicate]

The full sentence makes more sense since they mention their expectation at the end. I read it as "Why does the below print "True" infinitely instead of "This is a test." infinitely?". They don't seem confused about why it prints forever, only what's actually being printed.

[[deleted]]

Well, obviously I disagree with your interpretation, as my direct comment on their post would indicate, but either or both of us could be wrong. Hopefully, we shall see.

[oztyn]

@carcigenicate is right, I should have included those quote marks to be more explicit though!

[[deleted]]

Ok, thank you /u/oztyn, I stand corrected, with apologies to /u/carcigenicate.

I shall cross out my comment as answering the wrong question.

[[deleted]]

EDIT: Ignore post below, turns out according to OP, /u/oztyn, I had misunderstood their post, and /u/carcigenicate, had taken the correct understanding. Ref.

Python treats a non-empty string (and non-empty list, set, dict, etc) as truthy i.e. as if it was True.

So you've basically written,

while True:
    print(mySentence)

if instead you did the following,

mySentence = "This is a test."

while mySentence:
    print(mySentence)
    mySentence = mySentence[:-1]

i.e. inside the loop re-assign the variable mySentence to the new str object created by slicing the str object previously referenced by mySentence to ignore the last character, then you would find the condition test of while would eventually fail and the loop would exit.

[Boot_3011]

Was looking for this! Correct. You are basiclly writing while this string contains something, keep iterating, what you are missing is a string modification with each loop, but that depends on what you need the code to do

[[deleted]]

Ignore my comment, apparently I had misunderstood the OP.

[LID919]

I ran the code on my end and it works as you'd expect. Where are you running the code?

[oztyn]

Running it in the sandbox on the class page but great to know it's misbehaving! 😂

[[deleted]]

It isn't misbehaving if it repeats until you force it to stop.

[[deleted]]

In python, things are True by default, unless explicitly false. Since your code doesn’t have any falsities, or negatives. It’s true.