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.

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.

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.

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.