Understanding Python's bitwise NOT

Question

I was trying to understand bitwise NOT in python. I tried following:

>>> ~0b0
-1

>>> 0b1
1

Why is this the case? As per my understanding, ~0b0 is 0b1. But seems that python interprets it -1 in 2's complement, but 0b1 is getting interpreted as 1.

Why is this so? More importantly, how and why does python determines when to interpret number or MSB of binary string negative?

Answer 1

Python interprets a word of binary bits as a negative number when

a) the sign bit is set (the most significant bit of a word)

and

b) the str or repr method is called (to get the string representation or value representation of a word).

or, implicitly, any time you treat the word as a number.

Answer 2

Per-spec:

The unary ~ (invert) operator yields the bitwise inversion of its integer argument. The bitwise inversion of x is defined as -(x+1).

because semantically Python's integers are always signed and manipulated as two's complement.