Python Lambda Function

What are Lambda/anonymous Functions in Python?

Lambda is an anonymous function in Python. Python Lambda Function

There’s two ways to make functions in python: def and lambda.

Def is pretty straightforward, Functions may also be created with the lambda expression, a feature that allows us to in-line function definitions in places where a def statement won’t work syntactically.

Two key distinctions between a lambda expression and a def function:

  1. lambda is an expression, not a statement. Because of this, a lambda can appear in places a def is not allowed by Python’s syntax—inside a list literal or a function call’s arguments, for example. With def, functions can be referenced by name but must be created elsewhere.
  2. lambda’s body is a single expression, not a block of statements. Because it is limited to an expression, a lambda is less general than a def—you can only squeeze so much logic into a lambda body without using statements such as if.

Besides those distinctions, def and lambda are pretty similar.

Example

def adder(x, y, z): 
	return (x + y + z)

The equivalent syntax using a lambda expression would be:

f = lambda x, y, z: x + y + z

Lambda expressions are often used with map, reduce, and filter.

Lambda function with map()

map: It applies a given function to each item of an iterable and returns an iterator.

map(function, iterable)

numbers = [2, 3, 4, 5]  
squaredNum = list(map(lambda num: num ** 2 , numbers))  
  
print(squaredNum)  
[4, 9, 16, 25]

Lambda function with filter()

filter: It has the same syntax as the map function. It helps in extracting items from an iterable based on the given condition.

filter(function, iterable)

numbers = [2, 3, 4, 5]  
evenNum = list(filter( lambda num: num % 2 == 0 , numbers))  
  
print(evenNum)
[2, 4]

Example: Lambda function with reduce()

reduce: It applies a function cumulatively/successively on each item of an iterable and returns a single value.

reduce(function, iterable, [, initializer])

from functools import reduce

numbers = [1, 2, 3, 4, 5]
total = reduce(lambda x, y: x + y, nums)
print(total)

15

When do use lambda function ?

The best use case of a lambda expression is to pass a simple callable to functions such as sort, map, filter.

Python Lambda Function
  1. Lambda is an anonymous function in Python
  2. map: It applies a given function to each item of an iterable and returns an iterator.
  3. filter: It has the same syntax as the map function. It helps in extracting items from an iterable based on the given condition.
  4. reduce: It applies a function cumulatively/successively on each item of an iterable and returns a single value.