Creating an empty list in Python

Question

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    Technical reasons  as to which is faster   creating a class causes overhead   Code readability - which one is the standard convention

User · Accepted Answer

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.

User · Answer

list   is inherently slower than     because    there is symbol lookup  no way for python to know in advance if you did not just redefine list to be something else     there is function invocation   then it has to check if there was iterable argument passed  so it can create list with elements from it  ps  none in our case but there is  if  check   In most cases the speed difference won t make any practical difference though

User · Answer

Just to highlight  Darkonaut answer because I think it should be more visible  new list      or new list   list   are both fine  ignoring performance   but append   returns None  as result you can t do new list   new list append something

User · Answer

I use       It s faster because the list notation is a short circuit  Creating a list with items should look about the same as creating a list without  why should there be a difference

User · Answer

I do not really know about it  but it seems to me  by experience  that jpcgt is actually right  Following example  If I use following code  t        implicit instantiation t   t append 1    in the interpreter  then calling t gives me just  t  without any list  and if I append something else  e g   t   t append 2    I get the error   NoneType  object has no attribute  append    If  however  I create the list by   t   list     explicit instantiation   then it works fine

[python] Creating an empty list in Python

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