`lambda`

In Python, the lambda keyword creates anonymous functions, also known as lambda functions. These functions are defined using the lambda keyword followed by a list of parameters, a colon, and an expression. Python evaluates the expression and returns the result when you call the lambda function.

Python `lambda` Keyword Examples

Here’s a quick example of using the lambda keyword to provide the key function and sort a dictionary by values:

>>> students = {
...     "Alice": 89.5,
...     "Bob": 76.0,
...     "Charlie": 92.3,
...     "Diana": 84.7,
...     "Ethan": 88.9,
...     "Fiona": 95.6,
...     "George": 73.4,
...     "Hannah": 81.2,
... }

>>> dict(sorted(students.items(), key=lambda item: item[1]))
{
    'George': 73.4,
    'Bob': 76.0,
    'Hannah': 81.2,
    'Diana': 84.7,
    'Ethan': 88.9,
    'Alice': 89.5,
    'Charlie': 92.3,
    'Fiona': 95.6
}

In this example, you sort the dictionary by value in ascending order. To do this, you use a lambda function that takes a two-value tuple as an argument and returns the second item, which has an index of 1.

Python `lambda` Keyword Use Cases

Creating callables for operations that can be expressed in a single expression
Combining short anonymous functions with functions like map(), filter(), and reduce()
Performing small operations that are used only once or very locally within your code

Tutorial

How to Use Python Lambda Functions

In this step-by-step tutorial, you'll learn about Python lambda functions. You'll see how they compare with regular functions and how you can use them in accordance with best practices.

intermediate best-practices python

For additional information on related topics, take a look at the following resources: