I know that there is numpy.isnan() for checking if a value is float('nan') but I think that native python should logically return False in bool(float('nan')).

Do you have a particular use case for this? This is a backwards-incompatible change, and the existing behavior (the only false-y float being 0.0) is very old and well-established.

If this change was implemented, I suspect almost every use of it would benefit from a clarifying comment like

    if x: # check for NaNs
        ...

...so that is a hint to me that using the existing math.isnan() (or numpy.isnan() if you have numpy) is more explicit and therefore more readable.

I also think it would be confusing to have two different floats (0.0 and NaN) both be false-y.

Sorry, I'm just going to close this. For values of all numeric types now, `bool(x)` returns the same as `x != type(x)(0)`. Besides being backward-incompatible, making an exception for NaN would be jarringly inconsistent.

Note that you don't need numpy to conveniently check for a NaN anyway; Python's math.isnan() does the same.

If you want to persist, please bring it up on the python-ideas mailing list. If it gains traction there, feel free to re-open this report.