Reverse Iteration in Python

Introduction

In Python, we can use a for loop to iterate over a list and execute a function for each element. However, what if we want to start from the last element and work our way backwards? In this challenge, you will need to create a function that executes the provided function once for each list element, starting from the list's last element.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL python(("`Python`")) -.-> python/BasicConceptsGroup(["`Basic Concepts`"]) python(("`Python`")) -.-> python/ControlFlowGroup(["`Control Flow`"]) python(("`Python`")) -.-> python/DataStructuresGroup(["`Data Structures`"]) python(("`Python`")) -.-> python/FunctionsGroup(["`Functions`"]) python/BasicConceptsGroup -.-> python/comments("`Comments`") python/ControlFlowGroup -.-> python/for_loops("`For Loops`") python/DataStructuresGroup -.-> python/lists("`Lists`") python/DataStructuresGroup -.-> python/tuples("`Tuples`") python/FunctionsGroup -.-> python/function_definition("`Function Definition`") subgraph Lab Skills python/comments -.-> lab-13642{{"`Reverse Iteration in Python`"}} python/for_loops -.-> lab-13642{{"`Reverse Iteration in Python`"}} python/lists -.-> lab-13642{{"`Reverse Iteration in Python`"}} python/tuples -.-> lab-13642{{"`Reverse Iteration in Python`"}} python/function_definition -.-> lab-13642{{"`Reverse Iteration in Python`"}} end

Execute function for each list element in reverse

Write a function for_each_right(itr, fn) that takes a list itr and a function fn as arguments. The function should execute fn once for each element in itr, starting from the last one.

def for_each_right(itr, fn):
  for el in itr[::-1]:
    fn(el)

for_each_right([1, 2, 3], print) ## 3 2 1

Summary

In this challenge, you learned how to create a function that executes a provided function for each element in a list, starting from the last one. This can be useful when you need to process a list in reverse order.

Reverse Iteration in Python

Introduction

Skills Graph

Execute function for each list element in reverse

Summary

Other Python Tutorials you may like