Can someone give me an explanation why isinstance() returns True in the following case? I expected False, when writing the code.
print isinstance(True, (float, int))
True
My guess would be that its Python's internal subclassing, as zero and one - whether float or int - both evaluate when used as boolean, but don't know the exact reason.
What would be the most pythonic way to solve such a situation? I could use type() but in most cases this is considered less pythonic.
For historic reasons, bool is a subclass of int, so True is an instance of int. (Originally, Python had no bool type, and things that returned truth values returned 1 or 0. When they added bool, True and False had to be drop-in replacements for 1 and 0 as much as possible for backward compatibility, hence the subclassing.)
The correct way to "solve" this depends on exactly what you consider the problem to be.
True to stop being an int, well, too bad. That's not going to happen.If you want to detect booleans and handle them differently from other ints, you can do that:
if isinstance(whatever, bool):
# special handling
elif isinstance(whatever, (float, int)):
# other handling
If you want to detect objects whose specific class is exactly float or int, rejecting subclasses, you can do that:
if type(whatever) in (float, int):
# Do stuff.