Creating an empty list in Python

python performance list coding-style timeit
user225312 picture user225312 · Jun 4, 2010 · Viewed 706.1k times · Source

What is the best way to create a new empty list in Python?

l = []

or

l = list()

I am asking this because of two reasons:

  1. Technical reasons, as to which is faster. (creating a class causes overhead?)
  2. Code readability - which one is the standard convention.

Answer

unutbu picture unutbu · Jun 4, 2010

Here is how you can test which piece of code is faster:

% python -mtimeit  "l=[]"
10000000 loops, best of 3: 0.0711 usec per loop

% python -mtimeit  "l=list()"
1000000 loops, best of 3: 0.297 usec per loop

However, in practice, this initialization is most likely an extremely small part of your program, so worrying about this is probably wrong-headed.

Readability is very subjective. I prefer [], but some very knowledgable people, like Alex Martelli, prefer list() because it is pronounceable.

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