Python Lambda Functions

What are lambda functions in Python?

Lambda functions, also known as anonymous function are the functions without a name. As Python uses the def keyword to define the function, but to define a lambda function, we do not need to use the keyword def. A lambda function can take any number of arguments, but can only have one expression.

How to use lambda Functions in Python?

The syntax of the lambda function is:-
lambda arguments: expression

Example of Lambda Function in python

Let us be more clear with an example that shows the use of lambda function over normal function.


The output of the above program is:-

Normal Function square(): 25
Lambda Function sq(): 49
In the above program, we can see that one way of defining a function is to use def keyword and lambda function makes it easier to write such function in a single line of code. Here,  x is the argument and x * x is the expression. We can use multiple arguments in lambda function, but the expression should be only one.
Lambda functions can be used along with built-in functions like filter(), map() and reduce().

Use of Lambda Function with map()

map() function takes two arguments, viz. a function and a list. The function is called with a lambda function and a list and a new list is returned which contains all the lambda modified items returned by that function for each item.

For Example:

The output is:-

[4, 10, 38, 50, 68, 110]

Use of Lambda Function with filter()

The filter() function takes a function and a list as arguments. This offers an elegant way to filter out all the elements of a sequence “sequence”, for which the function returns True. Here is an example program that returns the even numbers from an input list:

The output of the program is:-

[10, 124, 450, 300, 304]

Use of Lambda Function with reduce()

The reduce() function takes a function and a list as arguments. The function is called with a lambda function and a list and a new reduced result is returned. This performs a repetitive operation over the pairs of the list. This is a part of the functools module.

The output of the program is:-

Sum = 1532
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