Understanding Python Lambda Expressions: Syntax, Examples, and Use Cases

When we need to do something simple and prefer quick work rather than formally naming a function, lambda expressions are ideal. Lambda expressions are also called anonymous functions.

In Python, lambda expressions are a short way to declare small anonymous functions (no need to give them a name).

Lambda functions behave like regular functions declared with def . They are useful for defining small functions concisely. They can only contain a single expression, so they are not suitable for functions with control‑flow statements.

Lambda function syntax

lambda arguments: expression

Lambda functions can have any number of arguments but only one expression.

Code examples

# Lambda function to compute the square of a number square = lambda x: x ** 2 print(square(3)) # Output: 9

# Traditional function to compute the square of a number def square1(num): return num ** 2 print(square1(5)) # Output: 25

In the lambda example, lambda x: x ** 2 creates an anonymous function object that is assigned to the name square , allowing it to be called like a regular function.

Lambda function examples

Basic

lambda_func = lambda x: x**2 # returns the square of an integer print(lambda_func(4)) # 16

Intermediate

lambda_func = lambda x: True if x**2 >= 10 else False print(lambda_func(3)) # False print(lambda_func(8)) # True

Complex

linuxmi_dict = {"X": 1, "Y": 2, "Z": 3} sorted_keys = sorted(linuxmi_dict, key=lambda i: linuxmi_dict[i] % 3) print(sorted_keys) # ['Z', 'X', 'Y']

Use case: filtering odd numbers from a list

Using a for loop:

linuxmi_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] filtered = [] for num in linuxmi_list: if num % 2 != 0: filtered.append(num) print(filtered) # [1, 3, 5, 7, 9, 11]

Using a list comprehension:

filtered = [x for x in linuxmi_list if x % 2 != 0]

Using the built‑in filter function with a lambda:

filtered = filter(lambda i: i % 2 != 0, linuxmi_list) print(list(filtered)) # [1, 3, 5, 7, 9, 11]

Note: In Python 3 the filter function returns a generator, so you must wrap it with list() to see the results; in Python 2 it returns a list directly.

The filter call applies the lambda to each element of linuxmi_list ; elements for which the lambda returns False are discarded, leaving only the odd numbers.