How can I cap or limit the length of an array in Python?

Question

I am attempting to create an array in python that is capped at 60 values. My array starts with 0 values and then every minute, it adds a value to the array. When a new value is added, I want the oldest value added, i.e the last to get removed when the newest value is added (keeping the length at 60). Here is (parts) of my code so far...

pList = []
i = 0
while(True):
  pcList.append(x)
  if(i >= 60):
    #??
  i = i + 1
  time.sleep(60)

I am unsure about how to go about removing the last (first value) when it gets to 60 values when adding a new one.

So you want to remove the oldest one a new value comes and the capacity is above 60? — Dani Mesejo, Feb 06 '19 at 01:37
Yup @MichaelButscher is spot in with the queue.Queue structure. However, if OP wants to use a list implementation they can look into list.pop(), list.insert() and/or list.append(). — Kyle, Feb 06 '19 at 01:41
@MichaelButscher almost certainly, the OP should use a `collections.deque` instead of a `queue.Queue` — juanpa.arrivillaga, Feb 06 '19 at 02:00
@juanpa.arrivillaga Oh, right, multithread support is overkill here. — Michael Butscher, Feb 06 '19 at 02:07
While there are duplicate questions, I'd suggest that the cited question isn't one. Yes, it addresses the stated goal, but it doesn't address the posted code or underlying question of basic list operations, but directs the user to an alternate solution. As an educational lesson for beginning programmers, addressing their code is important. — Chris Larson, Feb 06 '19 at 02:08
For eample, perhaps: https://stackoverflow.com/q/45572916/214150 — Chris Larson, Feb 06 '19 at 02:12

Chris Larson · Accepted Answer · 2019-02-06T01:53:34.240

As mentioned in the comments, there are other, better ways to accomplish this, but, answering your specific question, and correcting your code for a couple of issues, the following illustrates how to add and remove elements from a list, based on length of the list.

Note that I shortened your time to make it easier to watch the process take place.

Also, I replaced i's value as your test to the length of the list itself as the test, as your question specifies.

There's a typo at pcList.append(x) and that's corrected below to `pList.

import time

pList = []
i = 0
while(True):
  pList.append(i)
  if len(pList) >= 60:
    pList.pop(0)
  i = i + 1
  print(pList)
  time.sleep(.25)

How can I cap or limit the length of an array in Python?

1 Answers1