Python type hinting a deque filled with myclass objects

Question

using Python 3.6 or newer, I want to type hint a function myfunc that returns an object of MyClass.

How can I hint, that myqueue is a deque filled with MyClass objects?

from collections import deque

global_queue = deque()

class MyClass:
    pass

def myfunc(myqueue=global_queue) -> MyClass:
    return myqueue.popleft()

for i in range(10):
    global_queue.append(MyClass())

Answer 1

In Python 3.9, you can use deque['MyClass']() directly.

If you are using Python 3.6.1 or higher, you can use typing.Deque:

from typing import Deque
from collections import deque

global_queue: Deque['MyClass'] = deque()

class MyClass:
    pass

def myfunc(myqueue: Deque[MyClass] = global_queue) -> MyClass:
    return myqueue.popleft()

for i in range(10):
    global_queue.append(MyClass())

Alternatively, you can do global_queue = Deque['MyClass']() instead -- at runtime, that'll construct a collections.deque object.

If you need to support Python 3.5, install the typing_extensions 3rd party library and do from typing_extensions import Deque. That library contains backports of types that were added after the typing module was first added to the standard library.