PythonLambda Functions

Lambda Functions in Python

In Python, a lambda function is a small, anonymous function defined using the lambda keyword. Unlike regular functions created with def, lambda functions are typically used for simple, one-line operations.

Lambda functions are useful when you need a quick function — especially when passing functions as arguments.

Syntax of Lambda Function

lambda_syntax.py
lambda arguments: expression
  • lambda — keyword to define the anonymous function.
  • arguments — one or more parameters.
  • expression — a single expression whose result is returned.

Lambda functions do not contain multiple statements or complex logic — they must be written in one line.

Example 1: Basic Lambda Function

lambda_basic.py
square = lambda x: x * x
print(square(5))
output.txt
25

Explanation:

  • lambda x: x * x defines an anonymous function that returns the square of x.
  • The function is assigned to square and called like a normal function.

Example 2: Lambda with Two Parameters

lambda_two_params.py
add = lambda a, b: a + b
print(add(3, 7))
output.txt
10

Explanation:

  • Lambda function with two arguments: a and b.
  • Returns their sum.

Example 3: Using Lambda with map()

lambda_map.py
nums = [1, 2, 3, 4]
squares = list(map(lambda x: x * x, nums))
print(squares)
output.txt
[1, 4, 9, 16]

Explanation:

  • map() applies the lambda function to every element in the list.
  • The result is a list of squared numbers.

Example 4: Using Lambda with filter()

lambda_filter.py
nums = [1, 2, 3, 4, 5, 6]
even = list(filter(lambda x: x % 2 == 0, nums))
print(even)
output.txt
[2, 4, 6]

Explanation:

  • filter() applies the lambda function to each element.
  • It returns only those elements that satisfy the condition.

Example 5: Lambda Inside Sorted

lambda_sorted.py
names = ["Alice", "Bob", "Charlie", "David"]
sorted_names = sorted(names, key=lambda name: len(name))
print(sorted_names)
output.txt
['Bob', 'Alice', 'David', 'Charlie']

Explanation:

  • Lambda function used as key in sorted().
  • Sorts names based on their length.

Example 6: Lambda with Default Parameter

lambda_default.py
greet = lambda name="Guest": f"Hello, {name}"
print(greet())
print(greet("Alice"))
output.txt
Hello, Guest
Hello, Alice

Explanation:

  • You can use default parameters in a lambda function.

When to Use Lambda Functions

Use CaseExample
Simple, one-line transformationsmap(), filter(), sorted()
Passing function as argumentHigher-order functions
Quick, throwaway functionsShort anonymous operations
Avoiding full function definitionSave lines of code when logic is simple

Limitations of Lambda Functions

  • Can only contain one expression (no statements, no multiple lines).
  • Cannot include assignments or complex logic.
  • Readability may suffer if overused for complex operations.

Summary

  • Lambda functions are anonymous, one-line functions created with lambda.
  • They are ideal for short, simple tasks.
  • Commonly used with map(), filter(), and sorted().
  • For complex logic, prefer regular functions using def.

In the next section, we will explore Recursion — a powerful technique where functions call themselves to solve problems.

Variable ScopeRecursion