I found that ~True
is -2
and ~False
is -1
. Why is this?
W3Schools says that ~
inverts all the bits. Why isn't ~True
is False
and ~False
is True
?
My attempt to explain these:
True
is +1
, and the bits of +1
are inverted. +
is inverted to -
.
1
in two-digit binary is 01
, so inverted bits: 10
, ie 2
. So result is -2
.
False
is +0
, +
is inverted to -
, 0
in two-digit binary is 00
, all the bits inverted, 11
, which is 3
- it should be 1
.
This answer paints a more complicated picture:
A list full of Trues only contains 4- or 8-byte references to the one canonical True object.
The PyTables User’s Guide says:
bool: Boolean (true/false) types. Supported precisions: 8 (default) bits.
These don't support the simplistic (and apparently wrong) reasoning above.
First of all, I'd use the not
operator to invert Boolean values (not True == False
, and vice versa). Now if Booleans are stored as 8-bit integers, the following happens:
True
is 0000 0001. Hence ~True
yields 1111 1110, which is -2 in two's-complement representation.
False
is 0000 0000. Hence ~False
yields 1111 1111, which is -1.
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