pythonic way to do something N times without an index variable

Question

Every day I love python more and more    Today  I was writing some code like   for i in xrange N       do something     I had to do something N times  But each time didn t depend on the value of i  index variable   I realized that I was creating a variable I never used  i   and I thought  There surely is a more pythonic way of doing this without the need for that useless index variable    So    the question is  do you know how to do this simple task in a more  pythonic  beautiful way

User · Answer

since function is first-class citizen  you can write small wrapper  from Alex answers   def repeat f  N       for   in itertools repeat None  N   f     then you can pass function as argument

User · Answer

A slightly faster approach than looping on xrange N  is   import itertools  for   in itertools repeat None  N       do something

User · Answer

What about a simple while loop   while times  gt  0      do something       times -  1   You already have the variable  why not use it

User · Answer

Use the   variable  as I learned when I asked this question  for example     A long way to do integer exponentiation num   2 power   3 product   1 for   in xrange power       product    num print product

User · Answer

The   is the same thing as x  However it s a python idiom that s used to indicate an identifier that you don t intend to use  In python these identifiers don t takes memor or allocate space like variables do in other languages   It s easy to forget that   They re just names that point to objects  in this case an integer on each iteration

User · Answer

I found the various answers really elegant  especially Alex Martelli s  but I wanted to quantify performance first hand  so I cooked up the following script   from itertools import repeat N   10000000  def payload a       pass  def standard N       for x in range N           payload None   def underscore N       for   in range N           payload None   def loopiter N       for   in repeat None  N           payload None   def loopiter2 N       for   in map payload  repeat None  N            pass  if   name         main         import timeit     print  standard    timeit timeit  standard      format N           setup  from   main   import standard   number 1       print  underscore    timeit timeit  underscore      format N           setup  from   main   import underscore   number 1       print  loopiter    timeit timeit  loopiter      format N           setup  from   main   import loopiter   number 1       print  loopiter2    timeit timeit  loopiter2      format N           setup  from   main   import loopiter2   number 1     I also came up with an alternative solution that builds on Martelli s one and uses map   to call the payload function  OK  I cheated a bit in that I took the freedom of making the payload accept a parameter that gets discarded  I don t know if there is a way around this  Nevertheless  here are the results   standard   0 8398549720004667 underscore   0 8413165839992871 loopiter   0 7110594899968419 loopiter2   0 5891903560004721   so using map yields an improvement of approximately 30  over the standard  for loop and an extra 19  over Martelli s

User · Answer

I just use for   in range n   it s straight to the point  It s going to generate the entire list for huge numbers in Python 2  but if you re using Python 3 it s not a problem

User · Answer

Assume that you ve defined do something as a function  and you d like to perform it N times  Maybe you can try the following   todos    do something    N   for doit in todos        doit

[coding-style] pythonic way to do something N times without an index variable?

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