Annonymous functions (Lambda functions)

Sometimes, naming a function is not worth the trouble. For example when you’re sure the function will only be used once. For such cases, Python offers us anonymous functions, also called lambda functions.

A lambda function can be assigned to a variable, creating a concise way of defining a function:

add_one = lambda x: x + 1
add_one(3)
# 4

It gets more interesting when you need to use a function as an argument. In such cases, the function is often used only once. As you may know, map applies a function to all elements of an iterable object. We can use a lambda when calling map:

numbers = [1, 2, 3, 4]
times_two = map(lambda x: x * 2, numbers)
list(times_two)
# [2, 4, 6, 8]

In fact, this is a pattern that you’ll see often. When you need to apply a relatively simple operation on each element of an iterable object, using map() in combination with a lambda function is concise and efficient.