Groups > comp.lang.python > #19165

Re: verify the return value of a function

From	Terry Reedy <tjreedy@udel.edu>
Subject	Re: verify the return value of a function
Date	2012-01-20 15:42 -0500
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On 1/20/2012 10:07 AM, Steven D'Aprano wrote:

> What should be avoided, when possible, is over-reliance on isinstance
> checks instead of protocol or interface checks. For example, don't check
> for a list if your function doesn't *need* a list but would be happy with
> a tuple or some other sequence.

In other words, do not use isinstance to artificially limit the input 
domain of a function. The generic or polymorphic nature of (builtin) 
operators and functions is a major feature of Python.

On the other hand, the output range of a function is typically much more 
limited as to type. Complete testing requires testing the specified 
output type. For instance, sorted(iterable) is documented as producing a 
sorted list, so 'type(output) is list' is an appropriate test.

-- 
Terry Jan Reedy

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Re: verify the return value of a function Jean-Michel Pichavant <jeanmichel@sequans.com> - 2012-01-20 11:13 +0100
  Re: verify the return value of a function Mel Wilson <mwilson@the-wire.com> - 2012-01-20 08:53 -0500
    Re: verify the return value of a function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-01-20 15:07 +0000
      Re: verify the return value of a function Terry Reedy <tjreedy@udel.edu> - 2012-01-20 15:42 -0500

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