How to loop backwards in python

Question

I m talking about doing something like   for i n  i gt  1  --i         do something with i     I can think of some ways to do so in python  creating a list of range 1 n 1  and reverse it  using while and --i       but I wondered if there s a more elegant way to do it  Is there   EDIT  Some suggested I use xrange   instead of range   since range returns a list while xrange returns an iterator  But in Python 3  which I happen to use  range   returns an iterator and xrange doesn t exist

User · Answer

All of these three solutions give the same results if the input is a string:

1.

def reverse(text):
    result = ""
    for i in range(len(text),0,-1):
        result += text[i-1]
    return (result)

2.

text[::-1]

3.

"".join(reversed(text))

User · Answer

def reverse text       reversed          for i in range len text -1  -1  -1           reversed    text i      return reversed  print  reverse          format  abcd   reverse  abcd

User · Answer

for x in reversed whatever       do something     This works on basically everything that has a defined order  including xrange objects and lists

User · Answer

range   and xrange   take a third parameter that specifies a step  So you can do the following   range 10  0  -1    Which gives   10  9  8  7  6  5  4  3  2  1     But for iteration  you should really be using xrange instead  So   xrange 10  0  -1       Note for Python 3 users  There are no separate range and xrange functions in Python 3  there is just range  which follows the design of Python 2 s xrange

User · Answer

To reverse a string without using reversed or    -1   try something like   def reverse text         Container for reversed string     txet           store the length of the string to be reversed       account for indexes starting at 0     length   len text -1        loop through the string in reverse and append each character       deprecate the length index     while length gt  0          txet      s  text length          length- 1     return txet

[python] How to loop backwards in python?

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