Python Lambda Functions

Lambda functions are small anonymous functions, meaning they do not have a defined name. These are small, short-lived functions used to pass simple logic to another function.

• Contain only one expression.
• Result of that expression is returned automatically (no return keyword needed).

In this example, a lambda function is defined to convert a string to its upper case using upper().

GEEKSFORGEEKS

Explanation:

• 'a' store the string 'GeeksforGeeks'.
• upper is a lambda function that takes an argument x and returns x.upper().
• upper(a) applies the lambda to a, converting it to uppercase.

Syntax

Lambda functions are created using the lambda keyword. Below is the syntax:

• Function name (a): stores the lambda function so it can be reused later.
• Lambda keyword (lambda): defines an anonymous (inline) function.
• Argument (x): input value passed to the lambda function.
• Expression (x**2): operation performed on the argument and returned as the result.

Use Cases

1. Condition Checking: lambda function can use conditional expressions (if-else) to return different results based on a condition.

Positive
Negative
Zero

Explanation: lambda function takes x as input. It uses nested if-else statements to return "Positive," "Negative," or "Zero."

2. List Comprehension: Lambda can be combined with list comprehensions to apply the same operation to multiple values in a compact way.

10
20
30
40

Explanation: lambda function multiplies each element by 10. List comprehension iterates through range(1, 5) and applies the lambda to each value.

3. Returning Multiple Results: Although a lambda can contain only one expression, it can still return multiple results by combining them into a tuple.

(7, 12)

Explanation: lambda function performs both addition and multiplication and returns a tuple with both results.

4. filter(): This function uses a lambda expression to select elements from a list that satisfy a given condition, such as keeping only even numbers.

[2, 4, 6]

Explanation: lambda function checks if a number is even (x % 2 == 0) and filter() applies this condition to each element in the list c.

5. map(): This function applies a lambda expression to each element and returns a map object. It can be converted to a list using list().

[2, 4, 6, 8]

Explanation: lambda function doubles each number and map() iterates through a and applies the transformation.

6. reduce(): This function repeatedly applies a lambda expression to elements of a list to combine them into a single result.

24

Explanation: lambda multiplies two numbers at a time and reduce() applies this operation across the list.

To know the difference between def keyword and Lambda function, refer to this article, def vs lambda.