When to choose collections.Iterable or 'iter' attribute in Python?

Question

In this question there are numerous ways to test for an iterable. Two of the solutions are:

hasattr(object, '__iter__')
isinstance(object, collections.Iterable)

They both seem to do the same thing and I can't find any doc that differentiates them. What is the difference and why would I choose one over the other?

3. Try and iterate it and catch the exception if it fails. – khelwood Dec 20 '18 at 16:09 — khelwood, Dec 20 '18 at 16:09

score 4 · Answer 1 · answered Dec 20 '18 at 16:09

4

The pythonic way is

assume it is iterable
catch the exception if it is not

However, use it with common sense. That's, do it only if you have reason to believe that your object is iterable in the majority of cases.

Also, take care of strings, which are treated as iterables, but in most practical use cases, they should not be. In that case, the practice is to explicitly check isinstance(.., str)

answered Dec 20 '18 at 16:09

blue_note

27,712
9
72
90

1

This follows the [EAFP](https://docs.python.org/3/glossary.html#term-eafp) principle in Python. – Andrew F Dec 20 '18 at 16:12
1

@AndrewF: exactly. however, common sense should dictate whether that's appropriate, depending on the context – blue_note Dec 20 '18 at 16:13
@blue_note the question has been edited for clarity. – E.Beach Dec 21 '18 at 00:27

When to choose collections.Iterable or '__iter__' attribute in Python?

1 Answers1

When to choose collections.Iterable or 'iter' attribute in Python?