isinstance(False, int) returns True

Question

I want to determine if a variable is an integer, so I use the following code:

if isinstance(var, int):
    do_something()

but when var = False, the do_something function is executed.

when var = None, the isinstance() function works normaly.

yes. because `bool` objects are `int` objects. IOW `issubclass(bool, int) is True` — juanpa.arrivillaga, Mar 20 '20 at 07:16
Yes, it seems like the best way for me to check it the variable is exactly an integer is using: type(var) == int — Machine Markus, Mar 20 '20 at 07:27
More idiomatically, `type(var) is int`, since class objects are singletons, in any case, that is more a style issue (although it is slightly faster than using `==`). — juanpa.arrivillaga, Mar 20 '20 at 07:28
`issubclass(bool, int)` is also `True`. `bool` is a subclass of `int`. — Boseong Choi, Mar 20 '20 at 07:32

score 3 · Answer 1 · answered Mar 20 '20 at 07:34

Because bool is a subclass of int.
You can find it in builtins.py

class bool(int):
    """
    bool(x) -> bool

    Returns True when the argument x is true, False otherwise.
    The builtins True and False are the only two instances of the class bool.
    The class bool is a subclass of the class int, and cannot be subclassed.
    """

So issubclass(bool, int) also True.
isinstance(x, y) is True when x's type is a derived class of y's type.

score 1 · Answer 2 · answered Mar 20 '20 at 07:19

In Python3 boolean is defined as a subclass of integer.

That means True is equivalent to 1 where as False is equivalent to 0

You can find the more details here. The exact same explanation from that link is:

There are three distinct numeric types: integers, floating point numbers, and complex numbers. In addition, Booleans are a subtype of integers

score -1 · Answer 3 · answered Mar 20 '20 at 07:29

-1

Python treats True as 1 and False as 0. Now what you can do here is:

try:
    var = int(string(False))
except ValueError:
    print("Invalid Integer")

answered Mar 20 '20 at 07:29

Siddhant Shrivastav

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isinstance(False, int) returns True

3 Answers3