Type checking: an iterable type that is not a string

Question

To explain better, consider this simple type checker function:

from collections import Iterable
def typecheck(obj):
    return not isinstance(obj, str) and i         


        

Answer 1

In python 2.x, Checking for the __iter__ attribute was helpful (though not always wise), because iterables should have this attribute, but strings did not.

def typecheck(obj): return hasattr(myObj, '__iter__')

The down side was that __iter__ was not a truely Pythonic way to do it: Some objects might implement __getitem__ but not __iter__ for instance.

In Python 3.x, strings got the __iter__ attribute, breaking this method.

The method you listed is the most efficient truely Pythonic way I know in Python 3.x:

def typecheck(obj): return not isinstance(obj, str) and isinstance(obj, Iterable)

There is a much faster (more efficient) way, which is to check __iter__ like in Python 2.x, and then subsequently check str.

def typecheck(obj): return hasattr(obj, '__iter__') and not isinstance(obj, str)

This has the same caveat as in Python 2.x, but is much faster.