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Lambda Functions in Python

Overview

Lambda functions in Python are a way to create small, anonymous functions without having to define them using the standard def keyword. These functions are typically used for short periods of time and can be particularly useful when you need a simple function for a specific operation.

Characteristics of Lambda Functions

  • Single Line Function: Lambda functions are defined in a single line.
  • Multiple Arguments: They can take any number of arguments.
  • Single Expression: Lambda functions can only have one expression, which is evaluated and returned.
  • Anonymous: Lambda functions are anonymous, meaning they do not have a name unless assigned to a variable.

Syntax

The basic syntax for creating a lambda function is as follows:

lambda arguments : expression

Example

Here’s a simple example of a lambda function that adds 10 to a given number:

add_ten = lambda x: x + 10
print(add_ten(5))  # Output: 15

Built-in Functions with Lambda

Lambda functions are often used with Python’s built-in functions such as filter(), map(), and reduce().

1. filter()

The filter() function constructs an iterator from elements of an iterable for which a function returns true. A lambda function can be passed as the function argument to filter elements.

Example:

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
even_numbers = list(filter(lambda x: x % 2 == 0, numbers))
print(even_numbers)  # Output: [2, 4, 6, 8]

2. map()

The map() function applies a given function to all the items in an input list. You can use a lambda function to define the operation to be applied to each item.

Example:

numbers = [1, 2, 3, 4, 5]
squared_numbers = list(map(lambda x: x**2, numbers))
print(squared_numbers)  # Output: [1, 4, 9, 16, 25]

3. reduce()

The reduce() function is used to apply a particular function passed in its argument to all of the list elements. It’s part of the functools module.

Example:

from functools import reduce

numbers = [1, 2, 3, 4, 5]
sum_of_numbers = reduce(lambda x, y: x + y, numbers)
print(sum_of_numbers)  # Output: 15