Question

Is there a method like isiterable? The only solution I have found so far is to call

hasattr(myObj, '__iter__')

But I am not sure how fool-proof this is.

Answer 1

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):

   try:
       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.

2. 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')
   

3. 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__.