Python Lambda Functions: Anonymous Functions Explained

Sometimes you need a tiny function for just one quick task. Python Lambda Functions are perfect for these occasions. Writing a full def my_function(): block feels like overkill.

Enter the Lambda Function. It’s a way to write a function in a single line.

The Syntax

A lambda function can take any number of arguments, but can only have one expression. lambda arguments : expression

Normal Function vs. Lambda

# Normal way
def add_five(x):
    return x + 5

print(add_five(10))  # Output: 15

# Lambda way
add_five_lambda = lambda x : x + 5

print(add_five_lambda(10)) # Output: 15

When to Use Them

Lambdas are most powerful when used inside other functions that expect a function as an input, like map(), filter(), or sorting.

Example: Sorting by a specific key

Imagine you have a list of tuples, and you want to sort by the second item (the age).

students = [("Alice", 25), ("Bob", 20), ("Charlie", 30)]

# Sort by age (index 1)
# The lambda function takes a student 's' and returns 's[1]' (their age)
students.sort(key=lambda s: s[1])

print(students)
# Output: [('Bob', 20), ('Alice', 25), ('Charlie', 30)]

Without lambda, you’d have to write a separate function just to tell .sort() how to look at the age.