TIL how to create fixed-length iterables in Python using collections.deque with maxlen parameter. Perfect for creating circular buffers and bounded collections.

January 24, 2022 · 1 min · 66 words

If you want to create an iterable of a fixed length in python, use collections.deque with the maxlen parameter.

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import collections

fixed_list = collections.deque(5*[None], 10)

# this is now a fixed list of items 10.
# by _appending_ more items, you'd be dropping items
# from the beginning.

fixed_list.append(1)
print(fixed_list)

Note that this merely calls appendleft.