verify the return value of a function
Terry Reedy
tjreedy at udel.edu
Fri Jan 20 15:42:45 EST 2012
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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