Python Lambda Function Tutorial | Anonymous Function in Python

By Krunal Last updated Feb 2, 2019

In this example, we will see Python Lambda Function Tutorial | Anonymous Function in Python. You will learn what is it, its syntax and how to use it. In Python, anonymous or lambda function is the function that is defined without a name. While the standard functions are defined using a def keyword, in Python, the anonymous functions are defined using the lambda keyword.

Python Lambda Function Tutorial

The lambda function in python has the following syntax.

lambda arguments: expression

Lambda functions can have any number of arguments but only one expression. That expression is evaluated and returned. The Lambda functions can be used wherever the function objects are required.

Let’s see the following example.

# app.py

square = lambda x: x * x

print(square(5))

See the below output.

It behaves as a normal function and gives the output.

In the above program, lambda x: x * x is the lambda function. Here x is the argument and x * x is the expression that gets evaluated and returned.

Lambda function has no name. It returns the function object which is assigned to the identifier double. We can now call it a normal function. The statement is following,

square = lambda x: x * x

It is the same as

def square(x):
   return x * x

In Python, we generally use Lambda Function as an argument to the higher-order function which is a function that takes in other functions as arguments. Anonymous functions are used along with the built-in functions like filter(), map() etc.

Lambda Function with filter() Higher Order Function

Let’s take an example of Lambda Function with Higher Order Function.

# app.py

integers = range(1, 10)
even = list(filter(lambda x: x % 2 == 0, integers))
print(even)

In the first line, we have defined the integer list, and then we have used the filter higher order method and pass the lambda function which takes arguments of list one by one and then filter out the data and then return the list with filtered data.

Run the above code, and you will see the following example.

Lambda Function with map() Higher Order Function

The map() function in Python takes in the function and a list.

The Lambda function is called with all the items in a list, and a new list is returned which contains the items returned by that function for each item.

Here is the example use of map() function to square all the integers items in a list.

# app.py

integersList = range(1, 6)
squares = list(map(lambda x: x * x, integersList))
print(squares)

Above code take each integer from integersList and square all the items one by one and make a list and return that squared items list. So, it has mapped the list to the squared list. See the below output.

Finally, Python Lambda Function Tutorial or Anonymous Function in Python example is over.

Python