Python Reverse StringReverse the characters in a string. Use list comprehension, reverse and the join method.
Reverse string. Programs sometimes have unusual requirements. For example we might need to reverse the characters in a string. This could help for generating a unique key from some data.
With list comprehension, we get the characters of a string. And then we can reverse those characters with reverse() and call join() to join them back again.
List Comprehension
Example def. Here we introduce a reverse_string method. This method receives a string and returns a reversed form of it. We first use list comprehension to get a character list.
Tip With a list of characters, returned by the list comprehension, we can manipulate the ordering of the characters.
Reverse We invoke the list's reverse() method on the characters list. This changes the order of the letters in-place.
Join We join the characters together on an empty delimiter. This concatenates the chars into a new, reversed string.
Python program that implements string reverse method
def reverse_string(value): # Get characters from the string. characters = [c for c in value] # Reverse list of characters. characters.reverse() # Join characters back into string with empty delimiter. return "".join(characters) # Test our string reversal method. test1 = "cat" reversed1 = reverse_string(test1) print(test1) print(reversed1) test2 = "abcde" reversed2 = reverse_string(test2) print(test2) print(reversed2)
cat tac abcde edcba
Some concepts. Lists are powerful in Python. We can reverse them. With a list comprehension, meanwhile, we can quickly construct a list of characters from an expression.
List, strings
So The trick to manipulating strings is to convert them to lists first. We then just manipulate the list elements.
A review. By reversing strings, we learn how to manipulate strings in many ways. We can change the individual characters, or reorder the characters in any fashion. This is powerful.
© 2007-2021 sam allen.
see site info on the changelog.