[Introduction to Python] Lambda Expressions

[Introduction to Python] Lambda Expressions

Lambda expression is an anonymous function that returns some formatted data

The lambda expression syntax is as follows:

lambda parameters: expressions

i.e.

1. double = lambda num : num * 2

2. concat_first_letter = lambda a, b, c: a[0] + b[0] + c[0]

   concat_first_letter("World", "Wide", "Web")=>WWW

Lambda expressions must be written on one line, so they are more suitable for shorter functions that can be written on one line.

If you use conditional logic in a lambda expression, you must use the complete one if-else, and using it alone ifwill cause an error:

func = lambda num: "natural number" if num >= 0 else "negative number"

func(0) # 'natural number'

my_func = lambda num: "natural number" if num >= 0 # SyntaxError: invalid syntax

The advantage of using lambda expressions is that you can pass a function as a parameter to another function.

Lambda expression as parameter

Taking addition and multiplication as an example, the writing method using non-lambda is:

def add(n1, n2):
    return n1 + n2

def multiply(n1, n2):
    return n1 * n2

def calculator(operation, n1, n2):
    return operation(n1, n2)

calculator(multiply, 10, 20) # 200

calculator(add, 10, 20) # 30

The lambda expression is written as:

def calculator(operation, n1, n2):
    return operation(n1, n2)  # Using the 'operation' argument as a function

calculator(lambda n1, n2: n1 * n2, 10, 20) # 200
calculator(lambda n1, n2: n1 + n2, 10, 20) # 30

The same result will be more concise using lambda expressions, which is also the original intention of lambda expressions.

From the official Python documentation - Why can't lambda expressions contain statements? :

Unlike lambda forms in other languages, where they add functionality, Python lambdas are only a shorthand notation if you’re too lazy to define a function.

Lambdas in Python are designed to be lazy.

Application of lambda expressions to lists:

num_list = [0, 1, 2, 3, 4, 5]

list(map(lambda n: n ** 2, num_list)) # [0, 1, 4, 9, 16, 25]

list(filter(lambda n: n > 0, num_list)) # [1, 2, 3, 4, 5]