Anonymous / Lambda Function

In Python, anonymous function is a function that is defined without a name.

Normal functions are defined using the 'def' keyword.

Anonymous functions are defined using the 'lambda' keyword.

Rules of Lambda Function

Lambda functions are small functions usually not more than a line.

The body of lambda functions consists of only one expression.

Lambda functions can have any number of arguments just like a normal function.

The result of the expression is the value when the lambda is applied to an argument.

There is no need for any return statement in lambda function.

It cannot contain commands or multiple expressions.

Lambda functions have their own local namespace and cannot access variables other than those in their parameter list and those in the global namespace.

Syntax

    lambda [arg1,arg2,....,argn]:expression

Example 1: Normal Function

# Function to adds two numbers and returns the output
def add(x,y):
    return x + y

# Calling the Function
add(10,25)

Output:
35

Example 2: Lambda Function

# Lambda Function to adds two numbers,returns the output and called through the variable
sum = lambda x, y: x + y

# call the lambda function
print("Sum of two numbers : ",sum(10,25))   

Output:
Sum of two numbers :  35

Here we are using two arguments x and y.

Expression after colon is the body of the lambda function.

Lambda function has no name and is called through the variable it is assigned to.

(OR)

# Lambda Function to adds two numbers and returns the output 
(lambda x, y: x + y)(10,25)

Output:
35

Lambda functions along with built-in functions

Example 3 :

# Program to filter out only the odd items from a list
mylist = [1 , 5 , 15 , 22 , 58 , 98]
oddlist = list(filter(lambda x: (x%2 != 0), mylist))
print(oddlist)  

Output:
[1, 5, 15]

Example 4:

# Program to display cube of each item in a list using map()
mylist2 = [1, 2, 3, 4, 5, 6, 7]
cubelist = list(map(lambda x: x ** 3, mylist2))
print(cubelist) 

Output:
[1, 8, 27, 64, 125, 216, 343]