collections.deque doesn't have __iadd__ method. #2838

>>> from collections import deque
>>> d = deque()
>>> d += deque(range(3))
deque([0, 1, 2])

>>>>> from collections import deque
>>>>> d = deque()
>>>>> d += deque(range(3))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '+=' not supported between instances of 'deque' and 'deque'