Python map() Function

The map() function lets you apply a function to each item in a list, tuple, or any other iterable — all in one line. It's a very handy tool for data transformation and functional programming.

Syntax

map(function, iterable)

Parameters:

• function – A function to apply to each element of the iterable.
• iterable – A sequence (like a list, tuple, or string) whose items you want to process.

Returns:

• A map object (an iterator), which you can convert to a list or loop through.

Example: Square Numbers in a List

numbers = [1, 2, 3, 4]
squared = map(lambda x: x * x, numbers)
print(list(squared))

[1, 4, 9, 16]

Example: Convert Strings to Uppercase

words = ["apple", "banana", "cherry"]
uppercase_words = map(str.upper, words)
print(list(uppercase_words))

['APPLE', 'BANANA', 'CHERRY']

Use Case: Clean and Transform Data

Imagine you have a list of prices as strings and want to convert them to floats:

prices = ["10.5", "20.99", "5.00"]
prices_float = map(float, prices)
print(list(prices_float))

[10.5, 20.99, 5.0]

Using map() with Multiple Iterables

You can also use map() with two or more iterables:

a = [1, 2, 3]
b = [4, 5, 6]
sum_values = map(lambda x, y: x + y, a, b)
print(list(sum_values))

[5, 7, 9]

Common Mistakes

• Forgetting to convert the map object: map() returns an iterator, not a list by default.
• Not using a function: You must pass a valid function or lambda.
• Mismatch in length: If using multiple iterables, map() stops at the shortest one.

Interview Tip

map() is often used to clean or transform datasets in one line. It shows functional programming skills and saves you from writing verbose for loops.

Summary

• map() applies a function to each item of an iterable.
• Returns a map object (an iterator).
• Often used with lambda for quick transformations.
• Works with multiple iterables too.

Practice Problem

Write a program that takes a list of numbers and returns a new list with the cube of each number using map().

nums = [2, 3, 4]
cubes = map(lambda x: x**3, nums)
print(list(cubes))