How does casting works here?

Question

a='a'
b=bool(a)
print b
output-true

Answer 1

Anything other than
0, False & None
will evaluate true...
even bool(0.5) will result true...
edit:
also empty things will evaluate false...
like
bool("") = false
bool([]) = false.....etc

Answer 2

So far I see only empty string evaluates to False, any alphanumeric is casted into True, didn't test symbols & punctuation but I guess they too are regarded as True

Cmiiw

Answer 3

In python everything is an object. Objects like 0, None, False as mentioned above are treated as boolean false.
Talking about other object imagine that they are just containers. If container is empty (like empty string, or list) it is considered as boolean False:
>>> a, b = '', []
>>> bool(a)
False
>>> bool(b)
False

If container is NOT empty, it is considered as boolean TRUE, no matter whether it is numeric negative or zero, or space-filled string:
>>> x, y = -1, ' '
>>> bool(x)
True
>>> bool(y)
True
Even if this container contains an other empty element, the container itself is not empty, so it is consiered as boolean True:

>>> wow = [[]]
>>> bool(wow)
True

>>> yay = [[False]]
>>> bool(yay)
True