To reverse for loop in Python just need to read the last element first and then the last but one and so on till the element is at index 0. You can do it with the range function, List Comprehension, or reversed() function.
The most common way to repeat a specific task or operation N times is by using the for loop in programming. We can iterate the code lines N times using the for loop with the range() function in Python.
Python comes with a number of methods and functions that allow you to reverse a list, either directly or by iterating over the list object. You'll learn how to reverse a Python list by using the reversed() function, the . reverse() method, list indexing, for loops, list comprehensions, and the slice method.
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
andxrange
functions in Python 3, there is justrange
, which follows the design of Python 2'sxrange
.
for x in reversed(whatever):
do_something()
This works on basically everything that has a defined order, including xrange
objects and lists.
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))
def reverse(text):
reversed = ''
for i in range(len(text)-1, -1, -1):
reversed += text[i]
return reversed
print("reverse({}): {}".format("abcd", reverse("abcd")))
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>=0:
txet += "%s"%text[length]
length-=1
return txet
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