why does ~(True ^ False) return -2

Question

I tried the following command line in python

In[1]: ~(True ^ False)

and it returned :

Out[1]: -2

Could someone explain this to me please?

Thanks in advance

Does this answer your question? [The tilde operator in Python](https://stackoverflow.com/questions/8305199/the-tilde-operator-in-python) — n8sty, Jul 20 '20 at 16:02
(True ^ False) returned True (i.e. 1 in integer form). ~ operator is one's complement (for example : ~x => -(x+1)). So ~True or ~1 will be -(1+1) i.e. -2. — ClassHacker, Jul 20 '20 at 16:05

score 1 · Answer 1 · answered Jul 20 '20 at 16:01

1

It's because of how python handles booleans:

True is represented as 1, (See True==1)

False is represented as 0. (See False==0)

Without syntactic sugar and abstractions:

x=~(1 ^ 0)
x=~1
x=-2

answered Jul 20 '20 at 16:01

JCWasmx86

and why ~1 gives -2 – aka Jul 20 '20 at 16:06
It flips all bits. 1 is in binary `00000001`, if you apply bitwise not, it is changed to: `111111...(set bits)...111110`. Each set bit is unset and each unset bit is set now. – JCWasmx86 Jul 20 '20 at 16:12
One way to view tilde operator is as `~x = (-1) - x` – harold Jul 20 '20 at 16:12
But then if I replace with 2 numpy boolean arrays A and B of the same shape, ~(A ^ B) works well (i.e it returns an array of booleans). Why is it the case? – aka Jul 20 '20 at 16:26
1

@aka, the discrepancy you mention between pure Python and numpy is discussed here: https://joergdietrich.github.io/python-numpy-bool-types.html – dannyadam Jul 20 '20 at 19:35

1 Answers1