Is it possible to implement a Python for range loop without an iterator variable

Question

Is it possible to do following without the i   for i in range some number         do something   If you just want to do something N amount of times and don t need the iterator

User · Answer

What about   while range some number        do something

User · Answer

You may be looking for  for   in itertools repeat None  times         this is THE fastest way to iterate times times in Python

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We have had some fun with the following  interesting to share so    class RepeatFunction      def   init   self n 1   self n   n     def   call   self Func           for i in xrange self n               Func           return Func    ----usage k   0   RepeatFunction 7                         decorator for repeating function def Job        global k     print k     k    1  print  ---------  Job     Results     0 1 2 3 4 5 6 --------- 7

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If do something is a simple function or can be wrapped in one  a simple map   can do something range some number  times     Py2 version - map is eager  so it can be used alone map do something  xrange some number      Py3 version - map is lazy  so it must be consumed to do the work at all    wrapping in list   would be equivalent to Py2  but if you don t use the return   value  it s wastefully creating a temporary  possibly huge  list of junk    collections deque with maxlen 0 can efficiently run a generator to exhaustion without   storing any of the results  the itertools consume recipe uses it for that purpose  from collections import deque  deque map do something  range some number    0    If you want to pass arguments to do something  you may also find the itertools repeatfunc recipe reads well   To pass the same arguments   from collections import deque from itertools import repeat  starmap  args         my args here          Same as Py3 map above  you must consume starmap  it s a lazy generator  even on Py2  deque starmap do something  repeat args  some number    0    To pass different arguments   argses     1  2    3  4         deque starmap do something  argses   0

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Return first n items of the iterable as a list list itertools islice iterable  n     Taken from http   docs python org 2 library itertools html

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What everyone suggesting you to use   isn t saying is that   is frequently used as a shortcut to one of the gettext functions  so if you want your software to be available in more than one language then you re best off avoiding using it for other purposes   import gettext gettext bindtextdomain  myapplication     path to my language directory   gettext textdomain  myapplication       gettext gettext       print    This is a translatable string

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Instead of an unneeded counter  now you have an unneeded list  Best solution is to use a variable that starts with      that tells syntax checkers that you are aware you are not using the variable   x   range 5  while x    x pop     print  Work

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May be answer would depend on what problem you have with using iterator  may be use  i   100 while i      print i     i- 1   or   def loop N  doSomething       if not N          return     print doSomething N      loop N-1  doSomething   loop 100  lambda a a    but frankly i see no point in using such approaches

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You can use  11  or any number or another invalid identifier  to prevent name-colision with gettext  Any time you use underscore   invalid identifier you get a dummy name that can be used in for loop

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If you really want to avoid putting something with a name  either an iteration variable as in the OP  or unwanted list or unwanted generator returning true the wanted amount of time  you could do it if you really wanted   for type             x in range somenumber       dosomething     The trick that s used is to create an anonymous class type             which results in a class with empty name  but NB that it is not inserted in the local or global namespace  even if a nonempty name was supplied   Then you use a member of that class as iteration variable which is unreachable since the class it s a member of is unreachable

User · Answer

Off the top of my head  no   I think the best you could do is something like this   def loop f n       for i in xrange n   f    loop lambda   lt insert expression here gt   5    But I think you can just live with the extra i variable   Here is the option to use the   variable  which in reality  is just another variable   for   in range n       do something     Note that   is assigned the last result that returned in an interactive python session    gt  gt  gt  1 2 3  gt  gt  gt    3   For this reason  I would not use it in this manner  I am unaware of any idiom as mentioned by Ryan  It can mess up your interpreter    gt  gt  gt  for   in xrange 10   pass      gt  gt  gt    9  gt  gt  gt  1 2 3  gt  gt  gt    9   And according to Python grammar  it is an acceptable variable name   identifier      letter       letter   digit

User · Answer

I generally agree with solutions given above  Namely with     Using underscore in for-loop  2 and more lines  Defining a normal while counter  3 and more lines  Declaring a custom class with   nonzero   implementation  many more lines     If one is to define an object as in  3 I would recommend implementing protocol for with keyword or apply contextlib   Further I propose yet another solution  It is a 3 liner and is not of supreme elegance  but it uses itertools package and thus might be of an interest   from itertools import  chain  repeat   times   chain repeat True  2   repeat False   while next times       print  do stuff     In these example 2 is the number of times to iterate the loop  chain is wrapping two repeat iterators  the first being limited but the second is infinite  Remember that these are true iterator objects  hence they do not require infinite memory  Obviously this is much slower then solution  1  Unless written as a part of a function it might require a clean up for times variable

User · Answer

The general idiom for assigning to a value that isn t used is to name it     for   in range times       do stuff

User · Answer

Here s a random idea that utilizes  abuses   the data model  Py3 link    class Counter object       def   init   self  val           self val   val      def   nonzero   self           self val -  1         return self val  gt   0       bool       nonzero      Alias to Py3 name to make code work unchanged on Py2 and Py3  x   Counter 5  while x        Do something     pass   I wonder if there is something like this in the standard libraries

[python] Is it possible to implement a Python for range loop without an iterator variable?

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