mylist = list() vs mylist = [] in Python

Question

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Creating a list in Python- something sneaky going on?
Creating an empty list in Python

Consider the following:

mylist = list()

and:

mylist = []

Is there any benefit to using list() or [] - should one be used over the other in certain situation?

I'm inclined to think the [] literal would be faster since it saves a function call, but I've been wrong before. Did you try measuring this? — Frédéric Hamidi
@FrédéricHamidi -- I'm pretty sure I've seen this in a SO post before. I'll try to find it ... — mgilson
I haven't tried measuring, I will try and update soon, thanks Frederic — Sherlock
@FrédéricHamidi: Isn't it just syntactic sugar? In that case it probably wouldn't save a function call. — David Robinson

Sven Marnach Sven Marnach · Accepted Answer · 2012-08-02T15:06:26

For an empty list, I'd recommend using []. This will be faster, since it avoids the name look-up for the built-in name list. The built-in name could also be overwritten by a global or local name; this would only affect list(), not [].

The list() built-in is useful to convert some other iterable to a list, though:

a = (1, 2, 3)
b = list(a)

For completeness, the timings for the two options for empty lists on my machine (Python 2.7.3rc2, Intel Core 2 Duo):

In [1]: %timeit []
10000000 loops, best of 3: 35 ns per loop

In [2]: %timeit list()
10000000 loops, best of 3: 145 ns per loop

mylist = list() vs mylist = [] in Python

2 Answers