Trim a list to a maximum number of elements

Question

I would like to remove the oldest-added (i.e. the first) elements of a list, such that this list never exceeds 100 elements.

I thought about:

L = [327983, 232382, 1, 2, 3, 4, 5, 6, 23]

if len(L) > 100:
    for i in range(len(L)-100):
        del L[0]

print L    # [4, 5, 6, 23]

Is there a solution without iteration (or more generally: a nicer solution) for trimming the beginning of the list, so that it has <= 100 elements?

Sidenote: Isn't there something else than lists, for this purpose? i.e. a data structure that has a maximum size, and such that if more data comes, the oldest are deleted! (It makes me think about FIFO? Stack? Pipe?)

[Python Datatype for a fixed-length FIFO](https://stackoverflow.com/questions/1931589/python-datatype-for-a-fixed-length-fifo) — Cory Kramer, Jun 08 '15 at 12:47

score 8 · Answer 1 · answered Jun 08 '15 at 12:49

8

How about using collection.deque? If you specify maxlen, it will not store more than maxlen elements.

>>> from collections import deque
>>> q = deque([1, 2, 3], maxlen=3)
>>> q
deque([1, 2, 3], maxlen=3)
>>> q.append(4)
>>> q
deque([2, 3, 4], maxlen=3)

answered Jun 08 '15 at 12:49

falsetru

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score 4 · Accepted Answer · answered Jun 08 '15 at 12:45

4

You can just assign a slice back to your list

L = L[-100:]

answered Jun 08 '15 at 12:45

Cory Kramer

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Trim a list to a maximum number of elements

2 Answers2