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Python Lambda Functions

Python, known for its simplicity and readability, offers many built-in functions and syntactic constructs. One such feature is Python lambda functions, these allows for the creation of anonymous functions (typically short-lived functions, used at the point they are defined, that are not given a name).

What are Python Lambda Functions?

In Python, a lambda function is a small, anonymous function that can have any number of arguments, but can only have one expression. The expression is evaluated and returned when the function is called. Lambda functions are syntactically restricted to a single expression.

The general syntax is:

lambda arguments: expression

Why Use Lambda?

The primary use case for lambda functions is when you need a simple function for a short period and do not want to formally define it using the def keyword. This is especially useful when you’re working with functions like map(), filter(), and sorted(), which often require small, one-off functions to be passed to them.

A Simple Example

Let’s start with a basic example. Suppose you want to create a function that multiplies two numbers. Using the lambda function, it would look something like this:

multiply = lambda x, y: 
  x * y 

print(multiply(5, 3)) # Outputs: 15

Lambda with Built-in Functions

Lambda functions shine when used in conjunction with Python’s built-in functions. Let’s explore a few examples:

  1. Using map(): Suppose we have a list of numbers, and we want to square each number in the list.
numbers = [1, 2, 3, 4, 5] 
squared_numbers = list(map(lambda x: x**2, numbers)) 

print(squared_numbers) # Outputs: [1, 4, 9, 16, 25]
  1. Using filter(): Let’s say we want to filter out only the even numbers from a list.
numbers = [1, 2, 3, 4, 5]
even_numbers = list(filter(lambda x: x % 2 == 0, numbers))

print(even_numbers) # Outputs: [2, 4]
  1. Using sorted(): Imagine we have a list of tuples representing students and their scores, and we want to sort them based on scores.
students = [('Doug', 85), ('Bob', 78), ('Kate', 92)]
sorted_students = sorted(students, key=lambda x: x[1]) 

print(sorted_students) # Outputs: [('Bob', 78), ('Doug', 85), ('Kate', 92)]

Common Pitfalls

While lambda functions are powerful, they come with their own set of pitfalls:

  1. Overuse: Due to their concise nature, it’s tempting to use lambda functions everywhere. However, for more complex operations, it’s often more readable to use regular functions defined with def.
  2. Limited Expressivity: Lambda functions are restricted to a single expression. This means you can’t have multiple statements or include loops and conditionals in the traditional way.
  3. Debugging: Debugging can be slightly trickier with lambda functions since they don’t have a name. Errors will reference a lambda function, which might be harder to locate in a large codebase.


Lambda functions in Python offer a way to create small, anonymous functions on the fly. They’re especially handy for short-term use cases where defining a full function might feel overkill. However, like all tools, they have their place, and it’s essential to use them judiciously to maintain code clarity and readability.

Check out these resources to learn more: