1. Checking for __iter__ works on sequence types, but it would fail on e.g. strings in Python 2. I would like to know the right answer too, until then, here is one possibility (which would work on strings, too):

    from __future__ import print_function

    try: someobjectiterator = iter(someobject) except TypeError as te: print(someobject, 'is not iterable')

The iter built-in checks for the __iter__ method or in the case of strings the __getitem__ method.

  1. Another general pythonic approach is to assume an iterable, then fail gracefully if it does not work on the given object. The Python glossary:

Pythonic programming style that determines an object's type by inspection of its method or attribute signature rather than by explicit relationship to some type object ("If it looks like a duck and quacks like a duck , it must be a duck.") By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using type() or isinstance(). Instead, it typically employs the EAFP (Easier to Ask Forgiveness than Permission) style of programming.

...

>     try:
   _ = (e for e in my_object)
except TypeError:
   print my_object, 'is not iterable'
  1. The collections module provides some abstract base classes, which allow to ask classes or instances if they provide particular functionality, for example:

    from collections.abc import Iterable

    if isinstance(e, Iterable): # e is iterable

However, this does not check for classes that are iterable through __getitem__.