In Python, how do I determine if an object is iterable?

  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):

         some_object_iterator = iter(some_object)
     except TypeError as te:
         print(some_object, '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.

   _ = (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 import Iterable
     if isinstance(e, Iterable):
         # e is iterable

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

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