for or while loop to do something n times

Question

In Python you have two fine ways to repeat some action more than once  One of them is while loop and the other - for loop  So let s have a look on two simple pieces of code   for i in range n       do sth     And the other   i   0 while i  lt  n      do sth       i    1   My question is which of them is better  Of course  the first one  which is very common in documentation examples and various pieces of code you could find around the Internet  is much more elegant and shorter  but on the other hand it creates a completely useless list of integers just to loop over them  Isn t it a waste of memory  especially as far as big numbers of iterations are concerned   So what do you think  which way is better

User · Accepted Answer

but on the other hand it creates a completely useless list of integers just to loop over them. Isn't it a waste of memory, especially as far as big numbers of iterations are concerned?

That is what xrange(n) is for. It avoids creating a list of numbers, and instead just provides an iterator object.

In Python 3, xrange() was renamed to range() - if you want a list, you have to specifically request it via list(range(n)).

User · Answer

The fundamental difference in most programming languages is that unless the unexpected happens a for loop will always repeat n times or until a break statement   which may be conditional   is met then finish with a while loop it may repeat 0 times  1  more or even forever  depending on a given condition which must be true at the start of each loop for it to execute and always false on exiting the loop   for completeness a do     while loop   or repeat until   for languages that have it  always executes at least once and does not guarantee the condition on the first execution   It is worth noting that in Python a for or while statement can have break  continue and else statements where   break - terminates the loop continue - moves on to the next time around the loop without executing following code this time around else - is executed if the loop completed without any break statements  being executed   N B  In the now unsupported Python 2 range produced a list of integers but you could use xrange to use an iterator  In Python 3 range returns an iterator  So the answer to your question is  it all depends on what you are trying to do

User · Answer

This is lighter weight than xrange  and the while loop  since it doesn t even need to create the int objects  It also works equally well in Python2 and Python3  from itertools import repeat for i in repeat None  10       do sth

[python] for or while loop to do something n times

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