How to Run a for Loop in Reverse Order in Python

Normally, a ‘for’ loop in Python iterates over items of a sequence (like a list or a string) in the order that they appear. However, in some cases, you might need to iterate your sequence in reverse order. This tutorial will teach you how to run a ‘for’ loop in reverse order in Python.

Step 1: Understanding the ‘for’ Loop

A ‘for’ loop in Python is used for iterating over a sequence (that can be a list, tuple, string, dictionary, set, or range) or other iterable objects. In a traditional ‘for’ loop, iterating is done in the order the items appear in the sequence. Below is some simple code that uses a ‘for’ loop to print out each letter of a string:

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string = "Python"
 
for letter in string:
    print(letter)

Step 2: The ‘reversed()’ Built-In Python Function

To reverse a ‘for’ loop in Python, you can make use of the built-in Python function ‘reversed()’. This function returns a reversed iterator object from any sequence passed to it. Below is a snippet for reversing a string using ‘reversed()’.

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string = "Python"
 
for letter in reversed(string):
    print(letter)

Step 3: The [::-1] Slice Method

Another handy method for reversing a sequence in Python is using the [::-1] slicing method, which is a common method for reversing strings and lists in Python. You can use it to iterate through your sequence in reverse, as shown below:

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string = "Python"
 
for letter in string[::-1]:
    print(letter)

Output of the code

n
o
h
t
y
P

The Full Code

Here is the full code that demonstrates the two ways of reversing a ‘for’ loop in Python:

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# Using the reversed() function
string = "Python"
 
for letter in reversed(string):
    print(letter)
 
# Using the [::-1] slice method
string = "Python"
 
for letter in string[::-1]:
    print(letter)

Conclusion

So, there you have it! This tutorial has shown you not one, but two ways of reversing a ‘for’ loop in Python using the built-in function ‘reversed()’ and the [::-1] slice method. Mastering these techniques will be immensely useful in your Python programming journey. Remember, practice makes perfect, so keep coding!