collections.deque doesn't do anything useful

[hlovatt]

It looks like `deque` only has `append` and `popleft` and nothing else, therefore it doesn't do anything useful:

Code: Select all

MicroPython v1.16 on 2021-06-18; PYBD-SF2W with STM32F722IEK
Type "help()" for more information.
>>> from collections import deque
>>> d = deque((), 2)
>>> dir(d)
['__class__', 'append', 'popleft']
>>> d.append(1)
>>> d.popleft()
1
>>> d.append(2)
>>> d[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'deque' object isn't subscriptable
>>> d
<deque>
>>> for e in d:
...     print(e)
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'deque' object isn't iterable

1. You can't subscript it!
2. The `__repr__` for a `deque` isn't very helpful, just says "<deque>"!
3. You can't iterate it!

[hlovatt]

Re-reading my post I think I'm a bit harsh on deque; it does act as a FIFO, which is useful. However it is a long way from what you would expect a deque to do.

[pythoncoder]

See https://github.com/micropython/micropyt ... s/deque.py. There is nothing to stop you from extending its functionality further.

[mattyt]

This post reminded me that I had a minor patch to address some of the MicroPython-Lib deque shortcomings - so I've now opened a PR (that adds maxlen support). But I also want to add more deque features; feel free to help!