Add isiterable test cases for objects with __getitem__ method and with __iter__ set to None

Author: LincolnPuzey

toolz/tests/test_itertoolz.py

@@ -106,9 +106,34 @@ def test_unique():
 
 
 def test_isiterable():
+    # objects that have a __iter__() or __getitem__() method are iterable
+    # https://docs.python.org/3/library/functions.html#iter
+    class IterIterable:
+        def __iter__(self):
+            return iter(["a", "b", "c"])
+
+    class GetItemIterable:
+        def __getitem__(self, item):
+            return ["a", "b", "c"][item]
+
+    # "if a class sets __iter__() to None, the class is not iterable"
+    # https://docs.python.org/3/reference/datamodel.html#special-method-names
+    class NotIterable:
+        __iter__ = None
+
+    class NotIterableEvenWithGetItem:
+        __iter__ = None
+
+        def __getitem__(self, item):
+            return ["a", "b", "c"][item]
+
     assert isiterable([1, 2, 3]) is True
     assert isiterable('abc') is True
+    assert isiterable(IterIterable()) is True
+    assert isiterable(GetItemIterable()) is True
     assert isiterable(5) is False
+    assert isiterable(NotIterable()) is False
+    assert isiterable(NotIterableEvenWithGetItem()) is False
 
 
 def test_isdistinct():