Anonymous Functions in Python (Lambda Functions)

An anonymous function is a function without a name.
In Python, anonymous functions are created using the lambda keyword.
These are also called lambda functions.

They are small, one-line functions used for simple operations.

1. What is a Lambda Function?

A lambda function is a short, single-expression function that does not use def.

Syntax

lambda arguments: expression

Example:

square = lambda x: x * x
print(square(5))

Output:

2. Characteristics of Anonymous (Lambda) Functions

✔ No name (anonymous)
✔ One-line function only
✔ Can take multiple arguments
✔ Can be assigned to variables
✔ Often used inside other functions
✔ Faster for simple operations

But:

❌ Cannot contain multiple statements
❌ Cannot contain loops or complex logic
❌ Less readable for long operations

3. Why Use Lambda Functions?

Lambda functions are used when:

✔ A simple function is needed temporarily
✔ Used inside functions like map(), filter(), sorted()
✔ Avoid defining full def functions

They help write shorter and cleaner code.

4. Assigning a Lambda to a Variable

add = lambda a, b: a + b
print(add(10, 20))   # 30

5. Lambda with No Argument

msg = lambda: "Hello"
print(msg())

6. Lambda with Multiple Arguments

mul = lambda a, b, c: a * b * c
print(mul(2, 3, 4))

7. Lambda with Conditional Expression

max_num = lambda a, b: a if a > b else b
print(max_num(10, 20))

8. Lambda Inside Built-in Functions

A. Using lambda with `map()`

Applies a function to every element.

nums = [1, 2, 3, 4]
squares = list(map(lambda x: x * x, nums))
print(squares)

B. Using lambda with `filter()`

Filters elements based on condition.

evens = list(filter(lambda x: x % 2 == 0, nums))
print(evens)

C. Using lambda with `sorted()`

Sort list of tuples by second element.

pairs = [(1, 3), (2, 1), (5, 2)]
sorted_pairs = sorted(pairs, key=lambda x: x[1])
print(sorted_pairs)

9. Lambda in a User-Defined Function

def make_increment(n):
    return lambda x: x + n

inc = make_increment(5)
print(inc(10))   # 15

10. Limitations of Anonymous Functions

❌ Only one expression allowed
❌ Cannot use loops (for, while)
❌ Cannot include statements (if only as expression)
❌ Less readable for complex tasks

Therefore, use lambda for simple, short tasks only.

11. Practical Examples

Example 1: Find square

square = lambda x: x * x

Example 2: Check Even or Odd

check = lambda x: "Even" if x % 2 == 0 else "Odd"

Example 3: Add 10 to a number

add10 = lambda x: x + 10

Example 4: Maximum of three numbers

largest = lambda a, b, c: a if a > b and a > c else (b if b > c else c)

12. Difference: `def` vs `lambda`

`def` Function	Lambda Function
Can have multiple lines	Only one expression
Has a name	Anonymous
Supports loops	No loops
Supports complex logic	Simple logic
Better readability	Compact but less readable

Summary (for exam)

Anonymous functions are created using the lambda keyword.
They are single-expression, nameless functions used for short, temporary tasks.
Mostly used with map(), filter(), reduce(), sorted(), and inside other functions.

Anonymous functions