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Python: how to determine if an object is iterable?

Submitted by: @import:stackoverflow-api··
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objecthowiterabledeterminepython

Problem

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 foolproof this is.

Solution

-
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.

-
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')


-
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__.

Code Snippets

try:
    some_object_iterator = iter(some_object)
except TypeError as te:
    print(some_object, 'is not iterable')
try:
   _ = (e for e in my_object)
except TypeError:
   print(my_object, 'is not iterable')
from collections.abc import Iterable

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

Context

Stack Overflow Q#1952464, score: 1085

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