Python Lambda Functions

A lambda function is a small, anonymous function in Python that is designed to perform a simple operation.

Unlike a normal function created using def, a lambda function does not require a function name or a return statement.

Normal Function

def square(x):
    return x * x

print(square(5))

Lambda Function

square = lambda x: x * x

print(square(5))

Both produce:

25

Lambda functions are useful when the logic is short, simple, and needed for a small task.

Basic Syntax

lambda arguments: expression

For example:

lambda x: x * 2

Here:

• lambda → keyword used to create the lambda function
• x → parameter
• x * 2 → expression whose result is returned automatically

1. Creating a Simple Lambda Function

square = lambda x: x * x

print(square(5))

Output:

25

The lambda function:

lambda x: x * x

takes a number and returns its square.

2. Lambda with One Parameter

A lambda function can accept one parameter.

double = lambda x: x * 2

print(double(10))
print(double(25))

Output:

20
50

Another example:

cube = lambda x: x * x * x

print(cube(3))

Output:

27

3. Lambda with Multiple Parameters

A lambda function can accept multiple parameters.

add = lambda a, b: a + b

print(add(10, 20))

Output:

30

Another example:

multiply = lambda a, b: a * b

print(multiply(5, 6))

Output:

30

4. Lambda with Three Parameters

calculate = lambda a, b, c: a + b + c

print(calculate(10, 20, 30))

Output:

60

The number of parameters is not fixed.

lambda a: ...
lambda a, b: ...
lambda a, b, c: ...

5. Lambda with No Parameter

A lambda function can also have no parameters.

message = lambda: "Welcome to Python Bootcamp"

print(message())

Output:

Welcome to Python Bootcamp

Notice that the function is called using:

message()

because it doesn't require any arguments.

6. Lambda Automatically Returns the Result

With a normal function, we usually use return.

def add(a, b):
    return a + b

With lambda, the expression is automatically returned.

add = lambda a, b: a + b

So we don't write:

lambda a, b: return a + b

This is incorrect.

The correct syntax is:

lambda a, b: a + b

7. Lambda with Strings

Lambda functions can also work with strings.

get_length = lambda text: len(text)

print(get_length("Python"))
print(get_length("SkillMantra"))

Output:

6
11

Another example:

uppercase = lambda text: text.upper()

print(uppercase("python bootcamp"))

Output:

PYTHON BOOTCAMP

8. Lambda with String Concatenation

full_name = lambda first, last: first + " " + last

print(full_name("Rajendra", "Kandel"))

Output:

Rajendra Kandel

9. Lambda with Conditional Expression

Lambda can contain a conditional expression.

check = lambda x: "Positive" if x > 0 else "Negative"

print(check(10))
print(check(-5))

Output:

Positive
Negative

Another example:

check_age = lambda age: "Adult" if age >= 18 else "Minor"

print(check_age(25))
print(check_age(15))

Output:

Adult
Minor

10. Lambda for Even and Odd

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

print(check_number(10))
print(check_number(7))

Output:

Even
Odd

11. Lambda with Default Arguments

Lambda functions can have default values.

greet = lambda name="Student": "Hello " + name

print(greet())
print(greet("Raj"))

Output:

Hello Student
Hello Raj

The default value is used when no argument is provided.

12. Lambda with Multiple Default Arguments

calculate = lambda a=10, b=20: a + b

print(calculate())
print(calculate(50, 100))

Output:

30
150

13. Lambda Can Be Stored in a Variable

Although lambda functions are anonymous, we can assign them to variables.

greet = lambda: "Hello Python"

print(greet())

Here:

greet

holds a reference to the lambda function.

14. Multiple Lambda Functions

We can create several lambda functions.

add = lambda a, b: a + b subtract = lambda a, b: a - b multiply = lambda a, b: a * b

print(add(20, 10))
print(subtract(20, 10))
print(multiply(20, 10))

Output:

30
10
200

15. Lambda vs Normal Function

Normal Function

def square(number):
    return number * number

print(square(5))

Lambda Function

square = lambda number: number * number

print(square(5))

Both return:

25

Main Difference

16. Lambda with Function as an Argument

A lambda function itself can be passed to another function.

This is an important concept, but we are not covering map(), filter(), or other functions here.

Example:

def calculate(number, operation):
    return operation(number)


result = calculate(
    5,
    lambda x: x * x
)

print(result)

Output:

25

Here:

lambda x: x * x

is passed into the calculate() function.

Another example:

result = calculate(
    10,
    lambda x: x + 100
)

print(result)

Output:

110

17. Returning a Lambda from a Function

A normal function can return a lambda function.

def create_multiplier(number):

    return lambda x: x * number


double = create_multiplier(2)

print(double(10))
print(double(20))

Output:

20
40

Another example:

triple = create_multiplier(3)

print(triple(10))

Output:

30

This is a useful example of how Python functions can work with other functions.

18. Practical Example : Calculate Discount

discount = lambda price: price - (price * 0.10)

print(discount(1000))
print(discount(5000))

Output:

900.0
4500.0

The lambda applies a 10% discount.

19. Practical Example : Calculate Tax

calculate_tax = lambda price: price * 0.13

print(calculate_tax(1000))

Output:

130.0

20. Practical Example : Calculate Final Price

final_price = lambda price, discount: price - (price * discount / 100)

print(final_price(1000, 10))
print(final_price(5000, 20))

Output:

900.0
4000.0

21. Practical Example : Student Result

result = lambda marks: "Pass" if marks >= 40 else "Fail"

print(result(75))
print(result(35))

Output:

Pass
Fail

22. Practical Example : Grade Calculator

grade = lambda marks: (
    "A+" if marks >= 80
    else "A" if marks >= 70
    else "B+" if marks >= 60
    else "B" if marks >= 50
    else "Fail"
)

print(grade(85))
print(grade(72))
print(grade(45))

Output:

A+
A
Fail

For complicated grading logic, however, a normal function is generally easier to read.

23. Lambda with Boolean Results

A lambda can directly return True or False.

is_adult = lambda age: age >= 18

print(is_adult(25))
print(is_adult(15))

Output:

True
False

Another example:

is_even = lambda number: number % 2 == 0

print(is_even(10))
print(is_even(7))

24. Lambda with Mathematical Expressions

area = lambda length, width: length * width

print(area(10, 5))

Output:

50

Circle area:

circle_area = lambda radius: 3.14159 * radius * radius

print(circle_area(5))

25. When Should We Use Lambda?

Lambda functions are useful when:

• The operation is very short.
• The function is needed only for a small task.
• The logic can be expressed clearly in one expression.
• We want to pass a small function to another function.
• Creating a full def function would add unnecessary code.

Example:

square = lambda x: x * x

This is a good use of lambda because the logic is simple and immediately understandable.

26. When Should We Avoid Lambda?

Don't use lambda when the logic becomes complicated.

For example, instead of creating a very long lambda:

result = lambda x: ...

use:

def calculate_result(x):

    # complex logic here

    return result

A good rule for students:

If a lambda is difficult to read, use def instead.

Readable code is more important than writing fewer lines.

27. Important Rules of Lambda Functions

Remember these rules:

Rule 1 : Use the lambda keyword

lambda x: x * 2

Rule 2 : Parameters come before :

lambda x, y: x + y

Rule 3 : The expression comes after :

lambda x: x * x

Rule 4 : The result is automatically returned

square = lambda x: x * x

Rule 5 : Lambda is intended for simple expressions

Don't use it to write complicated business logic.

Copy Code

# ========================================== # Python Lambda Functions # ==========================================


# ------------------------------------------ # 1. Basic lambda function # ------------------------------------------

square = lambda x: x * x

print(square(5))


# ------------------------------------------ # 2. Lambda with one parameter # ------------------------------------------

double = lambda x: x * 2

print(double(10))
print(double(25))


# ------------------------------------------ # 3. Lambda with multiple parameters # ------------------------------------------

add = lambda a, b: a + b

print(add(10, 20))


# ------------------------------------------ # 4. Lambda with three parameters # ------------------------------------------

calculate = lambda a, b, c: a + b + c

print(calculate(10, 20, 30))


# ------------------------------------------ # 5. Lambda without parameters # ------------------------------------------

message = lambda: "Welcome to Python Bootcamp"

print(message())


# ------------------------------------------ # 6. Lambda with strings # ------------------------------------------

get_length = lambda text: len(text)

print(get_length("Python"))
print(get_length("SkillMantra"))


# ------------------------------------------ # 7. Convert string to uppercase # ------------------------------------------

uppercase = lambda text: text.upper()

print(uppercase("python bootcamp"))


# ------------------------------------------ # 8. String concatenation # ------------------------------------------

full_name = lambda first, last: first + " " + last

print(full_name("Rajendra", "Kandel"))


# ------------------------------------------ # 9. Lambda with condition # ------------------------------------------

check_age = lambda age: "Adult" if age >= 18 else "Minor"

print(check_age(25))
print(check_age(15))


# ------------------------------------------ # 10. Even or Odd # ------------------------------------------

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

print(check_number(10))
print(check_number(7))


# ------------------------------------------ # 11. Default argument # ------------------------------------------

greet = lambda name="Student": "Hello " + name

print(greet())
print(greet("Raj"))


# ------------------------------------------ # 12. Multiple default arguments # ------------------------------------------

calculate = lambda a=10, b=20: a + b

print(calculate())
print(calculate(50, 100))


# ------------------------------------------ # 13. Multiple lambda functions # ------------------------------------------

add = lambda a, b: a + b subtract = lambda a, b: a - b multiply = lambda a, b: a * b divide = lambda a, b: a / b

print(add(20, 10))
print(subtract(20, 10))
print(multiply(20, 10))
print(divide(20, 10))


# ------------------------------------------ # 14. Lambda with Boolean result # ------------------------------------------

is_adult = lambda age: age >= 18

print(is_adult(25))
print(is_adult(15))


# ------------------------------------------ # 15. Check even number # ------------------------------------------

is_even = lambda number: number % 2 == 0

print(is_even(10))
print(is_even(7))


# ------------------------------------------ # 16. Discount calculation # ------------------------------------------

discount = lambda price: price - (price * 0.10)

print(discount(1000))
print(discount(5000))


# ------------------------------------------ # 17. Tax calculation # ------------------------------------------

calculate_tax = lambda price: price * 0.13

print(calculate_tax(1000))


# ------------------------------------------ # 18. Final price calculation # ------------------------------------------

final_price = lambda price, discount: (
    price - (price * discount / 100)
)

print(final_price(1000, 10))
print(final_price(5000, 20))


# ------------------------------------------ # 19. Student result # ------------------------------------------

result = lambda marks: "Pass" if marks >= 40 else "Fail"

print(result(75))
print(result(35))


# ------------------------------------------ # 20. Grade calculator # ------------------------------------------

grade = lambda marks: (
    "A+" if marks >= 80
    else "A" if marks >= 70
    else "B+" if marks >= 60
    else "B" if marks >= 50
    else "Fail"
)

print(grade(85))
print(grade(72))
print(grade(45))


# ------------------------------------------ # 21. Mathematical calculation # ------------------------------------------

area = lambda length, width: length * width

print(area(10, 5))


# ------------------------------------------ # 22. Lambda as a function argument # ------------------------------------------

def calculate_number(number, operation):

    return operation(number)


result = calculate_number(
    5,
    lambda x: x * x
)

print(result)


# ------------------------------------------ # 23. Returning lambda from a function # ------------------------------------------

def create_multiplier(number):

    return lambda x: x * number


double = create_multiplier(2)

print(double(10))
print(double(20))


triple = create_multiplier(3)

print(triple(10))