Find All Matching Indexes (Challenge)

Introduction

In Python, we can use the enumerate() function to iterate over a list and get both the index and the value of each element. We can also use list comprehension to filter elements that satisfy a certain condition. In this challenge, you will use these concepts to create a function that finds the indexes of all elements in a list that satisfy a given testing function.

Skills Graph

Find All Matching Indexes

Problem

Write a function find_index_of_all(lst, fn) that takes a list lst and a testing function fn as arguments and returns a list of indexes of all elements in lst for which fn returns True.

Input

• A list lst of integers.
• A testing function fn that takes an integer as input and returns a boolean value.

Output

• A list of integers representing the indexes of all elements in lst for which fn returns True.

Example

find_index_of_all([1, 2, 3, 4], lambda n: n % 2 == 1) ## [0, 2]
find_index_of_all([1, 2, 3, 4], lambda n: n > 2) ## [2, 3]
find_index_of_all([1, 2, 3, 4], lambda n: n < 0) ## []

Note

• In the first example, the testing function lambda n: n % 2 == 1 checks if the integer is odd. The function returns [0, 2] because the elements at indexes 0 and 2 of the list [1, 2, 3, 4] are odd.
• In the second example, the testing function lambda n: n > 2 checks if the integer is greater than 2. The function returns [2, 3] because the elements at indexes 2 and 3 of the list [1, 2, 3, 4] are greater than 2.
• In the third example, the testing function lambda n: n < 0 checks if the integer is negative. The function returns [] because there are no negative elements in the list [1, 2, 3, 4].

Summary

In this challenge, you learned how to use enumerate() and list comprehension to find the indexes of all elements in a list that satisfy a given testing function. You can now use this knowledge to solve similar problems in the future.