Python Tutorial for Beginners: Lambda/Anonymous Function

Learn about lambda functions in Python in this tutorial. Discover how to create small, one-line functions that can be used to simplify your code.

In Python, a lambda function is a special type of function without the function name. For example,

lambda : print('Hello World')

Here, we have created a lambda function that prints 'Hello World'.

Before you learn about lambdas, make sure to know about Python Functions.

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Python lambda Function Declaration

We use the lambda keyword instead of def to create a lambda function. Here’s the syntax to declare the lambda function:

lambda argument(s) : expression 

Here,

• argument(s) – any value passed to the lambda function
• expression – expression is executed and returned

Let’s see an example,

greet = lambda : print('Hello World')

Here, we have defined a lambda function and assigned it to the variable named greet.

To execute this lambda function, we need to call it. Here’s how we can call the lambda function

# call the lambda
greet()

The lambda function above simply prints the text 'Hello World'.

Note: This lambda function doesn’t have any arguments.

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Example: Python lambda Function

# declare a lambda function
greet = lambda : print('Hello World')

# call lambda function
greet()

# Output: Hello World

In the above example, we have defined a lambda function and assigned it to the greet variable.

When we call the lambda function, the print() statement inside the lambda function is executed.

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Python lambda Function with an Argument

Similar to normal functions, the lambda function can also accept arguments. For example,

# lambda that accepts one argument
greet_user = lambda name : print('Hey there,', name)

# lambda call
greet_user('Delilah')

# Output: Hey there, Delilah

In the above example, we have assigned a lambda function to the greet_user variable.

Here, name after the lambda keyword specifies that the lambda function accepts the argument named name.

Notice the call of lambda function,

greet_user('Delilah')

Here, we have passed a string value 'Delilah' to our lambda function.

And finally, the statement inside the lambda function is executed.