[Numpy-discussion] help! type 'float64scalar' is not type 'float'

Christopher Barker Chris.Barker at noaa.gov
Thu Aug 3 12:33:54 CDT 2006

Sebastian Haase wrote:
> Finally I traced the problem down to a utility function:
> "is_number" - it is simply implemented as
> def is_number(val):
>      return (type(val) in [type(0.0),type(0)])

> OK - how should this have been done right ?

Well, as others have said, python is uses "duck typing", so you really 
shouldn't be checking for specific types anyway -- if whatever is passed 
in acts like it should, that's all you need not know. However, sometimes 
it does make sense to catch the error sooner, rather than later, so that 
it can be obvious, or handled properly, or give a better error message, 
or whatever.

In this case, I still use a "duck typing" approach: I don't need to know 
exactly what type it is, I just need to know that I can use it in the 
way I want, and an easy way to do that is to turn it into a known type:

def is_number(val):
	return True
     except ValueError:
	return False

Though more often, I'd just call float on it, and pass that along, 
rather than explicitly checking

This works at least with numpy float64scalar and float32scalar, and it 
should work with all numpy scalar types, except perhaps the long types 
that don't fit into a Python float.

it'll also turn string into floats if it can, which may or may not be 
what you want.


Christopher Barker, Ph.D.
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Chris.Barker at noaa.gov

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