Why isn't __add__ implemented in Python's deque?

问题

Concatenating two deques results in a TypeError.

from collections import deque
q = deque()
q + q

But __iadd__ is implemented so += is supported.

q1 = deque([1])
q2 = deque([2])
q1 += q2

What is the reason that only __iadd__ get implemented?

回答1:

This is a bug which is already fixed in the repos, so it should be included in the next released version of Python (3.5).

来源：https://stackoverflow.com/questions/32547316/why-isnt-add-implemented-in-pythons-deque