and vs list and dict which is better

Question

I understand that they are both essentially the same thing  but in terms of style  which is the better  more Pythonic  one to use to create an empty list or dict

User · Answer

there is one difference in behavior between    and list   as example below shows  we need to use list   if we want to have the list of numbers returned  otherwise we get a map object  No sure how to explain it though   sth     1 2    3 4   5 6   sth2   map lambda x  x 1   sth   print sth2    print returns object  lt map object at 0x000001AB34C1D9B0 gt   sth2    map lambda x  x 1   sth   print sth2    print returns object  lt map object at 0x000001AB34C1D9B0 gt  type sth2    list  type sth2 0     map  sth2   list map lambda x  x 1   sth   print sth2    2  4  6  type sth2    list type sth2 0     int

User · Answer

In my opinion    and    are the most pythonic and readable ways to create empty lists dicts   Be wary of set   s though  for example   this set    5  some other set        Can be confusing  The first creates a set with one element  the second creates an empty dict and not a set

User · Answer

It s mainly a matter of choice most of the time  It s a matter of preference   Note however that if you have numeric keys for example  that you can t do   mydict   dict 1  foo   2  bar     You have to do   mydict     1   foo    2   bar

User · Answer

The dict literal might be a tiny bit faster as its bytecode is shorter   In  1   import dis In  2   a   lambda     In  3   b   lambda  dict    In  4   dis dis a    1           0 BUILD MAP                0               3 RETURN VALUE  In  5   dis dis b    1           0 LOAD GLOBAL              0  dict                3 CALL FUNCTION            0               6 RETURN VALUE   Same applies to the list vs

User · Answer

list   and    work differently   gt  gt  gt  def a p           print id p         gt  gt  gt  for r in range 3           a          139969725291904 139969725291904 139969725291904  gt  gt  gt  for r in range 3           a list         139969725367296 139969725367552 139969725367616  list   always create new object in heap  but    can reuse memory cell in many reason

User · Answer

A box bracket pair denotes one of a list object  or an index subscript  my List x    A curly brace pair denotes a dictionary object    a list     on    off   1  2   a dict     on  1  off  2

User · Answer

IMHO  using list   and dict   makes your Python look like C   Ugh

User · Answer

In the case of difference between    and list    there is a pitfall that I haven t seen anyone else point out   If you use a dictionary as a member of the list  the two will give entirely different results   In  1   foo dict     1   foo    2   bar    In  2    foo dict  Out  2      1    foo    2    bar     In  3   list foo dict  Out  3     1    2

User · Answer

In terms of speed  it s no competition for empty lists dicts    gt  gt  gt  from timeit import timeit  gt  gt  gt  timeit       0 040084982867934334  gt  gt  gt  timeit  list     0 17704233359267718  gt  gt  gt  timeit       0 033620194745424214  gt  gt  gt  timeit  dict     0 1821558326547077   and for non-empty    gt  gt  gt  timeit   1 2 3    0 24316302770330367  gt  gt  gt  timeit  list  1 2 3     0 44744206316727286  gt  gt  gt  timeit  list foo    setup  foo  1 2 3    0 446036018543964  gt  gt  gt  timeit    a  1   b  2   c  3    0 20868602015059423  gt  gt  gt  timeit  dict a 1  b 2  c 3    0 47635635255323905  gt  gt  gt  timeit  dict bar    setup  bar    a   1     b   2     c   3     0 9028228448029267   Also  using the bracket notation lets you use list and dictionary comprehensions  which may be reason enough

[python] [] and {} vs list() and dict(), which is better?

Examples related to python

Examples related to performance

Examples related to list

Examples related to dictionary