Lambda Functions in Python

A Lambda function in Python is a small anonymous function. It is used to perform short and simple operations in a single line.

1. What is a Lambda Function?

A lambda function is a short function that normally does not have an explicit function name. Therefore, it is also called an anonymous function bhi kehte hain.

lambda x: x * 2

This function x takes as input and x * 2 returns

2. Normal Function vs Lambda

The same operation can be performed using both a normal function and a lambda.

Normal Function:

def square(number):
    return number * number

print(square(5))

Lambda Function:

square = lambda number: number * number

print(square(5))

Output:

25

3. Lambda Syntax

lambda arguments: expression

4. Lambda with One Argument

double = lambda x: x * 2

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

Output:

20
50

5. Lambda with Multiple Arguments

add = lambda a, b: a + b

print(add(10, 20))
print(add(50, 30))

Output:

30
80

6. Lambda with Three Arguments

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

print(total(10, 20, 30))

Output:

60

7. Lambda with Condition

A conditional expression can also be used in a lambda.

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

print(check(10))
print(check(7))

Output:

Even
Odd

8. Lambda with Maximum Number

maximum = lambda a, b: a if a > b else b

print(maximum(10, 25))

Output:

25

9. Lambda with List

A lambda can also be used with list data.

numbers = [1, 2, 3, 4, 5]

square = lambda x: x * x

for number in numbers:
    print(square(number))

Output:

1
4
9
16
25

10. Lambda with map()

map() is used to apply an operation to each element of a list.

numbers = [1, 2, 3, 4, 5]

squares = list(
    map(lambda x: x * x, numbers)
)

print(squares)

Output:

[1, 4, 9, 16, 25]

11. Lambda with filter()

filter() is used to select elements that satisfy a condition.

numbers = [1, 2, 3, 4, 5, 6]

even_numbers = list(
    filter(lambda x: x % 2 == 0, numbers)
)

print(even_numbers)

Output:

[2, 4, 6]

12. Lambda with sorted()

A lambda can also be used to define a custom sorting rule.

students = [
    ("Amit", 85),
    ("Rahul", 72),
    ("Sneha", 92)
]

students.sort(
    key=lambda student: student[1]
)

print(students)

Output:

[('Rahul', 72), ('Amit', 85), ('Sneha', 92)]

13. Lambda with Descending Sort

students = [
    ("Amit", 85),
    ("Rahul", 72),
    ("Sneha", 92)
]

students.sort(
    key=lambda student: student[1],
    reverse=True
)

print(students)

Output:

[('Sneha', 92), ('Amit', 85), ('Rahul', 72)]

14. CIIT Example 📩🤓

Suppose we have marks of CIIT students and we only want to filter the passing students.

marks = [35, 48, 72, 29, 65, 80]

passing_marks = list(
    filter(lambda mark: mark >= 40, marks)
)

print(passing_marks)

Output:

[48, 72, 65, 80]

15. CIIT Course Example 📩

courses = [
    ("Python", 35000),
    (".NET", 40000),
    ("Java", 38000)
]

courses.sort(
    key=lambda course: course[1]
)

print(courses)

Output:

[('Python', 35000), ('Java', 38000), ('.NET', 40000)]

16. Lambda Automatically Returns Result

In a lambda function, return keyword explicitly does not need to be written explicitly. The result of the expression is returned automatically.

square = lambda x: x * x

print(square(6))

Output:

36

17. Lambda Function Limitations

• A lambda is generally suitable for a single expression.
• A normal function is better for complex business logic.
• Excessive use of lambda can reduce code readability.
• A large function with multiple statements is not suitable for a lambda.

18. Normal Function vs Lambda

19. Common Mistakes

# Wrong

square = lambda x:
    return x * x

Normal multi-line return syntax is not used inside a lambda.

# Correct

square = lambda x: x * x

print(square(5))

Another Example:

# Avoid unnecessarily complex lambda

result = lambda x: (x * 2 + 10) if x > 5 else (x * 3 - 2)

If the logic is becoming complex, it is better to use a normal def def function.

20. Interview Points

• What is a lambda function?
• Why is a lambda called an anonymous function?
• What is the syntax of a lambda function?
• How many expressions are allowed in a lambda?
• What is the difference between a lambda and a normal function?
• How do you use a lambda with map() ?
• How do you use a lambda with filter() ?
• How is a lambda used in sorting?