Why is False not False in Python?-CodePudding

I was checking some of CPython's tests and in this file I saw a test case which was strange to me:

def test_math(self):
    ...
    self.assertIsNot( False, False)

At first I thought it is a typo and it should be self.assertIs( False, False) but when I tried it on the Python console the result was False:

>>>  False is False
<stdin>:1: SyntaxWarning: "is" with a literal. Did you mean "=="?
False
>>> 
>>> id(False)
140078839501184
>>> id( False)
140078839621760

Why does make it a different object?

Comments suggest that False is 0. So maybe the better question should be why is this?

CodePudding user response：

Because a bool is a type of int:

>>> isinstance(False, int)
True
>>> False == 0
True

a bool is accepted by functions that take ints as inputs (including all the standard operators), and those functions will generally return ints:

>>> True   False
1
>>> True * 2
2
>>> True ** False
1

or sometimes floats:

>>> True / True
1.0

Specifically, putting in front of a number is a "unary plus", the opposite of a "unary minus" which returns the negative of its operand:

>>>  True
1
>>> -True
-1
>>>  False
0
>>> -False
0

Although this bool/int behavior catches most people off guard the first time they find it, it allows for some useful shortcuts; for example, you can sum a bunch of bools to find the number of True values:

>>> sum([True, True, False, False, True])
3
>>> sum(s.startswith("a") for s in ("apple", "banana", "pear", "avocado"))
2

CodePudding user response：

When you apply arithmetic operations to boolean values they are turned into int.

In [10]: type( False)                                                                                                                                                                                                                   
Out[10]: int

In [11]: type(False)                                                                                                                                                                                                                    
Out[11]: bool

CodePudding user response：

False is equal to 0 and 0 is a literal. since you are not allowed to use is with literals(because they are not stored in memory), you get the warning.