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 -- http://mail.python.org/mailman/listinfo/python-list
