Understanding the `map` Function in Python

I recently attended an open online course on writing Python code in a more Pythonic way. Today's lesson was about lists.

When a two-dimensional list mylist containing integers is given as a parameter to the solution function, you can write the function to return a list containing the lengths of each element in mylist as follows:

def solution(mylist):
    res = []
    for i in mylist:
        res.append(len(i))
    return res

solution([[1, 2], [3, 4], [5]])
# Output: [2, 2, 1]

However, this can be written more concisely using the map function:

Using the map function allows you to apply a function to each element of a list without using a loop, making the code more concise and, in some cases, improving performance.

def solution(mylist):
    return list(map(len, mylist))

solution([[1, 2], [3, 4], [5]])
# Output: [2, 2, 1]

The map function applies the specified function to each element of one or more iterables and returns the results as a new iterable. Note that map returns a map object, so you need to convert it to a list or another type to view the result.

Structure of the map function

map(function, iterable, ...)

• function: The function to apply to each element. It usually takes one argument, but it can take multiple arguments when multiple iterables are used.
• iterable: The iterable(s) that map will iterate over while applying the function.

Example 1: Applying a function to each element of a list

def square(x):
    return x * x

numbers = [1, 2, 3, 4, 5]
squared = map(square, numbers)

print(list(squared))

This code applies the square function to every element in the numbers list and prints the result.

Example 2: When the function takes multiple arguments

def add(x, y):
    return x + y

numbers1 = [1, 2, 3]
numbers2 = [4, 5, 6]
added = map(add, numbers1, numbers2)

print(list(added))
# Output: [5, 7, 9]

In this example, the add function takes two arguments from numbers1 and numbers2 and returns their sum. For instance, the first elements of numbers1 and numbers2 are paired together and passed to the add function.

Using the map function allows you to apply a function to elements from multiple iterables in a concise manner, making the code more readable and easier to maintain.