False matching with 0 in a list python [duplicate]

Question

this line evaluates to True in python

False in [0,1,2]

because False and 0 are equal after typecasting. Is there any way to avoid this typecasting? Something like === operator for list?

(I know that I can handle this case with a loop by explicitly checking for value types, but I am curious if there is some short and sweet trick to do this without a loop).

Answer 1

First of all, there is no typecasting in Python. False == 0 is true because bool is a subclass of int, and the two objects really are equal.

And no, there is no === operator, you need to explicitly test for types if you don't want this to happen:

lst = [....]
testvalue = False
if any(testvalue == elem and type(testvalue) is type(elem) for elem in lst):
    # lst contains testvalue and it is the same type

This explicitly asserts that the two objects are the exact same type, disallowing for subclasses.

Yes, this is a loop. But in for a list also uses a loop, only internally, and both the in containment check and any() short circuit, they return True as soon as the first match is found.

Note that this would disallow float equality too. 0.0 == 0 is true too, but by testing for exact types you disallow that as well. The same goes for complex numbers, and Decimal():

>>> 0j == 0 == 0.0 == Decimal('0')
True

bool is just another numeric type here, albeit one limited to the numeric values 0 and 1.

The better approach, going forward, is to use type hinting in your code; the type hints checker would catch issues like you using booleans where integers or numbers are expected.