How can I check if an object is an iterator in Python?

Question

I can check for a next() method, but is that enough? Is there an ideomatic way?

Answer 1

To be an iterator an object must pass three tests:

• obj has an __iter__ method
• obj has a next method (or __next__ in Python 3)
• obj.__iter__() returns obj

So, a roll-your-own test would look like:

def is_iterator(obj):
    if (
            hasattr(obj, '__iter__') and
            hasattr(obj, 'next') and      # or __next__ in Python 3
            callable(obj.__iter__) and
            obj.__iter__() is obj
        ):
        return True
    else:
        return False