Python map()

numbers = [2, 4, 6, 8, 10]

# returns the square of a number
def square(number):
  return number * number

# apply square() to each item of the numbers list
squared_numbers_iterator = map(square, numbers)

# converting to list
squared_numbers = list(squared_numbers_iterator)
print(squared_numbers)

# Output: [4, 16, 36, 64, 100]

map() Syntax

Its syntax is:

map(function, iterable, ...)

map() Arguments

The map() function takes two arguments:

• function - a function
• iterable - an iterable like sets, lists, tuples, etc

You can pass more than one iterable to the map() function.

map() Return Value

The map() function returns an object of map class. The returned value can be passed to functions like

• list() - to convert to list
• set() - to convert to a set, and so on.

Example 1: Working of map()

def calculateSquare(n):
    return n*n


numbers = (1, 2, 3, 4)
result = map(calculateSquare, numbers)
print(result)

# converting map object to set
numbersSquare = set(result)
print(numbersSquare)

Output

<map object at 0x7f722da129e8>
{16, 1, 4, 9}

In the above example, each item of the tuple is squared.

Since map() expects a function to be passed in, lambda functions are commonly used while working with map() functions.

A lambda function is a short function without a name. Visit this page to learn more about Python lambda Function.

Example 2: How to use lambda function with map()?

numbers = (1, 2, 3, 4)
result = map(lambda x: x*x, numbers)
print(result)

# converting map object to set
numbersSquare = set(result)
print(numbersSquare)

Output

<map 0x7fafc21ccb00>
{16, 1, 4, 9}

There is no difference in functionalities of this example and Example 1.

Example 3: Passing Multiple Iterators to map() Using Lambda

In this example, corresponding items of two lists are added.

num1 = [4, 5, 6]
num2 = [5, 6, 7]

result = map(lambda n1, n2: n1+n2, num1, num2)
print(list(result))

Output

[9, 11, 13]