Lambda Expressions: A Quick Start

In Python, a lambda expression (or lambda function) is a way to create small, one-time, anonymous function objects. They are often used for small, one-time operations where a full function definition would be overly verbose.

The syntax for a lambda expression is:

lambda arguments: expression

Here, arguments is a comma-separated list of arguments, and expression is a single Python expression that is returned by the lambda.

Code Examples

1. Basic Lambda Function

A simple lambda that takes an argument and multiplies it by 2:

f = lambda x: x * 2
print(f(7))  # Outputs: 14

2. Multiple Arguments

A lambda that takes two arguments and adds them:

add = lambda x, y: x + y
print(add(5, 3))  # Outputs: 8

3. Conditionals

Using a lambda with a conditional expression:

check = lambda x: "Even" if x % 2 == 0 else "Odd"
print(check(4))  # Outputs: Even

4. Using Lambdas with map()

Applying a lambda to each element of a list:

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

5. Using Lambdas with filter()

Filtering a list with a lambda:

numbers = [1, 2, 3, 4, 5, 6]
evens = filter(lambda x: x % 2 == 0, numbers)
print(list(evens))  # Outputs: [2, 4, 6]

6. Sorting with Lambda

Sorting a list of tuples by the second element:

pairs = [(1, 2), (3, 1), (5, 10), (7, 5)]
pairs.sort(key=lambda x: x[1])
print(pairs)  # Outputs: [(3, 1), (1, 2), (7, 5), (5, 10)]

7. Nested Lambda Functions

Using lambdas within lambdas:

nested = lambda x: (lambda y: x + y)
add_five = nested(5)
print(add_five(3))  # Outputs: 8

8. Using Lambda with reduce()

Reducing a list using a lambda:

from functools import reduce
numbers = [1, 2, 3, 4, 5]
result = reduce(lambda x, y: x * y, numbers)
print(result)  # Outputs: 120

9. Combining Lambdas

Combining multiple lambda functions:

multiply = lambda x: x * 2
add_ten = lambda x: x + 10
result = lambda x: add_ten(multiply(x))
print(result(5))  # Outputs: 20

10. Lambda as an Argument

Passing a lambda as an argument to another function:

def apply_func(func, value):
    return func(value)

result = apply_func(lambda x: x + 5, 10)
print(result)  # Outputs: 15

Summary

Lambda expressions in Python provide a concise way to create small, anonymous functions. They can be used in a variety of contexts, from simple arithmetic to more complex operations like sorting and filtering. While lambdas are powerful, their use should be limited to situations where they enhance code clarity, as overuse can make code harder to understand.