Lambda Functions: The Secret Functions

Hello, young coder! Today, we’re going to uncover a secret in Python called lambda functions. Imagine a superhero with a special power that they use only when needed, without anyone knowing their real identity. That’s exactly what a lambda function is – a small, anonymous (secret) function that you can create quickly to do something specific.

What is a Lambda Function?

In Python, a lambda function is a tiny, unnamed function. Instead of using the def keyword to define a function, we use the lambda keyword. It’s like a quick, one-time use function.

Here’s how we normally define a function:

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

And here’s how we do the same thing with a lambda function:

add = lambda a, b: a + b

Both of these do the same thing – they add two numbers together. The difference is that the second one is using a lambda function.

Why Use Lambda Functions?

Lambda functions are great for small tasks where you don’t need to define a full function. They are often used when you need a simple function for a short period.

How to Create a Lambda Function

A lambda function in Python looks like this:

lambda arguments: expression

• lambda: This keyword is used to declare a lambda function.
• arguments: These are the inputs to the function, just like in a regular function.
• expression: This is what the function returns. It can only be a single line of code.

Examples of Lambda Functions

Let’s look at some examples to understand lambda functions better.

1. Adding Two Numbers

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

2. Multiplying Two Numbers

multiply = lambda x, y: x * y
print(multiply(4, 2))  # Output: 8

3. Checking if a Number is Even

is_even = lambda x: x % 2 == 0
print(is_even(4))  # Output: True
print(is_even(7))  # Output: False

4. Finding the Length of a String

length = lambda s: len(s)
print(length("hello"))  # Output: 5

Using Lambda Functions with Built-in Functions

Lambda functions are often used with Python’s built-in functions like map(), filter(), and sorted().

• map(): Applies a function to all items in an input list.

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

• filter(): Filters the input list based on 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]

• sorted(): Sorts the input list based on a key.

points = [(1, 2), (3, 1), (5, 7), (2, 3)]
sorted_points = sorted(points, key=lambda point: point[1])
print(sorted_points)  # Output: [(3, 1), (1, 2), (2, 3), (5, 7)]

Practice Questions

Now, let’s practice writing some lambda functions. Try to solve these problems on your own!

1. Create a lambda function that subtracts two numbers.
2. Create a lambda function that checks if a number is positive.
3. Use map() with a lambda function to double all the numbers in a list.
4. Use filter() with a lambda function to keep only the strings with more than 3 characters.

Solutions

Here are the solutions to the practice questions:

1. Subtracting Two Numbers

subtract = lambda x, y: x - y
print(subtract(10, 3))  # Output: 7

2. Checking if a Number is Positive

is_positive = lambda x: x > 0
print(is_positive(5))  # Output: True
print(is_positive(-1))  # Output: False

3. Doubling All Numbers in a List

numbers = [1, 2, 3, 4]
doubled = list(map(lambda x: x * 2, numbers))
print(doubled)  # Output: [2, 4, 6, 8]

4. Filtering Strings with More than 3 Characters

words = ["hi", "hello", "hey", "goodbye"]
long_words = list(filter(lambda word: len(word) > 3, words))
print(long_words)  # Output: ['hello', 'goodbye']

Lambda functions are like little secret agents in Python. They’re quick, efficient, and perfect for small tasks. Now that you know how to use them, you can add a new tool to your Python toolkit. Keep practicing, and soon you’ll be a lambda function master!