Specifing arguments type for a function

[Maric Michaud]

Le Mardi 20 Juin 2006 12:29, Rony Steelandt a écrit :
> What about
> def f(arg):
>     if type(arg)=='list':
>         #do something

And if arg's type is subclass of list ?
The problem with isinstance is : and if arg is not of type list but is a 
sequence (a instance of UserList for example) ?

The general case in python is duck typing, that means you define apis that 
accept file-like object, iterables, dict-like (mapping) objects, string like 
objects...

The problem with iterables is that they don't all implement the __iter__ 
attribute, for compatibility purpose the right test should be :

if not getattr(arg, '__iter__') and not getattr(arg, '__getitem__') :
    raise ValueError('Function accepts only iterables') # or error handling 
code


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Maric Michaud
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