22. Lambda Functions

Lambda functions are inline functions which have only 1 statement. They are created by using the keyword lambda They do not have any name, so they are also known as Anonymous functions. Although they don’t have a name, they can be bound to a variable.

A simple lambda function to greets us 👋:

greet = lambda: "Hello Pythonist!"

print(greet())

Hello Pythonist!

The above lambda function can be rewritten as a regular function as:

def greet():
    return "Hello Pythonist!"

print(greet())

Hello Pythonist!

Conceptually, lambda functions are similar to regular functions which are defined using def, just that lambda function accepts only 1 statement.

Let’s try calling lambda function without assigning the function to any variable.

print((lambda: "Hello Pythonist! ♥️")())

Hello Pythonist! ♥️

In the above example, we are creating the lambda expression enclosed in parenthesis and calling the function by using () at the end. As there is no name for the lambda function we just called, this is the reason why Lambda expressions/functions are also called as Anonymous functions.

We can pass parameters as well to the lambda function

add = lambda a, b: a + b
print(add(3, 5))

8

Till now, everything about lambda functions and regular functions do look the same, Is there any difference? Yup, here it is, Lambda functions do have the Lexical closures similar to loops in regular functions. What the heck is Lexical closure 🤔? At the end of the lexical scope, the value is still remembered unlike in the programming languages C, Golang etc.. Let’s try it out with an example 🙂

def do_sum(value):
    return lambda a: a + value

adder_3 = do_sum(3)
adder_10 = do_sum(10)

print(adder_3(5))
print(adder_10(5))

8
15

Here we can see that adder_3 and adder_10 are persisting the values that 3 and 10 that we passed during calling the do_sum function which returned the lambda function which holds our 3 and 10.