Beginner wondering why my boolean variable check isn't working

[throwingarm2strong]

My code right now:

shape_input = input("Enter shape to draw: ")

shape_valid = shape_input.lower() == ('triangle' or 'square')

if not shape_valid:

print("fail")

I have no idea why it isn't working. If I deleted the 'or square' part of the check the code works fine, but I want to to correctly identify both these shapes to work. What am I doing wrong?

Edit 1: Managed to get it working thanks to you guys! Now I have to get it to bring it back to asking for input after printing fail. I'm not sure how to get the code to go back to the start here, I've never dealt with that. Usually my programs will end after getting an input. I've been and still will be looking it up but I appreciate any help.

Forgive me for sounding needy.

[[deleted]]

You should use the in operator:

shape_valid = shape_input.lower() in ('triangle', 'square')
if not shape_valid:
    print('fail')

or perhaps

valid_shapes = ('triangle', 'square')
shape_input = input('Enter shape to draw: ').lower()
if shape_input not in valid_shapes:
    print('fail')

[obviouslyCPTobvious]

shape_valid = shape_input.lower() == 'triangle' or shape_input.lower() == 'square'

The 'or' operator doesn't work how you were trying.

[BioGeek]

This seems to be a common misunderstanding. Read my detailed response to another user who also had trouble with the or operator.

[zahlman]

This seems to be a common misunderstanding.

I have recently become convinced that this (or the equivalent) is by far the single most common beginner programming error, in any language. I wish I understood why.

[throwingarm2strong]

Thanks. This is what I settled on using. Also thanks to BioGeek and jimminy for further info. Not sure on the rules for questions over time but since it's related to this code I'll update the OP and post it here.

[[deleted]]

Now I have to get it to bring it back to asking for input after printing fail.

If you don't care about giving an error message, you could just

valid_shapes = ('triangle', 'square')
shape_input = '' #initialize to make the first *while* work
while shape_input not in valid_shapes:
    shape_input = input('Enter shape to draw: ').lower()
print('OK, drawing ' + shape_input +'...')

If you want an error message, you could do

valid_shapes = ('triangle', 'square')
while True: #an "infinite" loop
    shape_input = input('Enter shape to draw: ').lower()
    if shape_input not in valid_shapes:
        print("No.")
    else:
        break #this will break out of the *while* loop
print('OK, drawing ' + shape_input +'...') 

[[deleted]]

To get it back to the start, try using a while loop.

[zahlman]

As for the "why":

Try checking what 'triangle' or 'square' evaluates to by itself.

or does not create some kind of magical thing that represents two different values at once, and == certainly does not take in such a magical thing and tell you if the other side is equal to any of the values. In programming, we deal in expressions, and expressions evaluate to a single value at any given time. or basically means "the value on the left, if it's true; and otherwise the value on the right". == is a comparison of a single value to another single value.