len() should always return something

Diez B. Roggisch deets at nospam.web.de
Sat Jul 25 03:55:26 EDT 2009

Dr. Phillip M. Feldman schrieb:
> Here's a simple-minded example:
> def dumbfunc(xs):
>    for x in xs:
>       print x
> This function works fine if xs is a list of floats, but not if it is single
> float.  It can be made to work as follows:
> def dumbfunc(xs):
>    if isinstance(xs,(int,float,complex)): xs= [xs]
>    for x in xs:
>       print x
> Having to put such extra logic into practically every function is one of the
> annoying things about Python.

And where comes "len(xs)" into play here? What you want is iteration 
over scalars.

I do think that if you frequently have to write code like that, you are 
writing errorneous code.

But might that as it is, a simple

def iterable(i):
     if isinstance(i, (int, float, complex)):
        return [i]
     return i

is all you need. So you can write

for x in iterable(xs):

wherever you expect values to be either scalar or iterable.


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