Why do we use pop(0) instead of pop()?

Question

Why do we take the elements from the start of the list (https://teamtreehouse.com/library/objectoriented-python/hacknslash/game-planning), and don't use pop() method with no arguments? In this case, we would take items from the list from the end and speed would be always equal to O(1), and if you take elements from the beginning of the list, the performance will be O(n) because we have to move all elements of a list one step to the left. In this example, it will not affect speed, but if there is a huge list, remove items from start of list, not an optimal solution.

Answer 1 · 2016-10-08T23:29:17Z

October 8, 2016 11:29pm

Nice observation! You are correct in that the performance of pop(0) is significantly slower than pop() for large lists (above 10,000 elements). See timeit results below.

I believe Kenneth Love chose to pop from the front of the list as a straight-forward logical approach without trying to optimize for performance. Since the order of monsters in the list is arbitrary, popping from the back or the front isn't a requirement and either approach would work functionally.

Using timeit in the python REPL:

>>> import timeit
>>> stmt1 = "while foo: it = foo.pop();"
>>> stmt2 = "while foo: it = foo.pop(0);"
# Run on 1000 element list
>>> setup = "foo = list(range(1000))"
>>> timeit.timeit(stmt1, setup)
0.051728010177612305
>>> timeit.timeit(stmt2, setup)
0.05761384963989258
# Run on 10,000 element list
>>> setup = "foo = list(range(10000))"
>>> timeit.timeit(stmt1, setup)
0.05236983299255371
>>> timeit.timeit(stmt2, setup)
0.06780695915222168
# Run on 100,000 element list
>>> setup = "foo = list(range(100000))"
>>> timeit.timeit(stmt1, setup)
0.0552210807800293
>>> timeit.timeit(stmt2, setup)
1.3619050979614258
# Run on 1,000,000 element list
>>> setup = "foo = list(range(1000000))"
>>> timeit.timeit(stmt1, setup)
0.10635495185852051
>>> timeit.timeit(stmt2, setup)
226.78901600837708

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evgenypanov

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Why do we use pop(0) instead of pop()?

1 Answer

Chris Freeman

Chris Freeman

evgenypanov

evgenypanov