It is because bool is a subclass of int in both Python 2 and 3.
>>> issubclass(bool, int)
True
But the int implementation has changed.
In Python 2, int was the one that was 32 or 64 bits, depending on the system, as opposed to arbitrary-length long.
In Python 3, int is arbitrary-length – the long of Python 2 was renamed to int and the original Python 2 int dropped altogether.
In Python 2 you get the exactly same behaviour for long objects 1L and 0L:
Python 2.7.15rc1 (default, Apr 15 2018, 21:51:34)
[GCC 7.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.getsizeof(1L)
28
>>> sys.getsizeof(0L)
24
The long/Python 3 int is a variable-length object, just like a tuple – when it is allocated, enough memory is allocated to hold all the binary digits required to represent it. The length of the variable part is stored in the object head. 0 requires no binary digits (its variable length is 0), but even 1 spills over, and requires extra digits.
I.e. 0 is represented as binary string of length 0:
<>
and 1 is represented as a 30-bit binary string:
<000000000000000000000000000001>
The default configuration in Python uses 30 bits in a uint32_t; so 2**30 - 1 still fits in 28 bytes on x86-64, and 2**30 will require 32;
2**30 - 1 will be presented as
<111111111111111111111111111111>
i.e. all 30 value bits set to 1; 2**30 will need more, and it will have internal representation
<000000000000000000000000000001000000000000000000000000000000>
As for True using 28 bytes instead of 24 – you need not worry. True is a singleton and therefore only 4 bytes are lost in total in any Python program, not 4 for every usage of True.