Step 7¶

In Step 7, we will explore functions in Python. Functions are reusable blocks of code that perform a specific task. They help us organize our code, make it more readable, and avoid repetition.

Defining Functions¶

To define a function in Python, we use the def keyword (short for "define") followed by the function name and parentheses ().

Inside the parentheses, we can specify parameters, or "inputs", that the function can accept. The function body is indented and contains the code that will be executed when the function is called.

Syntax¶

def function_name(parameters):
    # code block to be executed

Example¶

def greet(name):
    print(f"Hello, {name}!")

In this example, greet is the function name, and name is a parameter. The function prints a greeting message using the provided name.

Calling Functions¶

To call a function, we use the function name followed by parentheses (). If the function accepts parameters, we pass the arguments inside the parentheses.

Example¶

greet("Alice")

This will output:

Hello, Alice!

Return Statement¶

Functions can return a value using the return statement. This allows us to capture the result of a function and use it in other parts of our code.

Example¶

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

result = add(3, 5)
print(result)

This will output:

Default Parameters¶

We can define default values for parameters in a function. If an argument is not provided when the function is called, the default value will be used.

Example¶

def greet(name="World"):
    print(f"Hello, {name}!")

greet()

This will output:

Hello, World!

by default, the function uses "World" as the name. If we call the function without providing a name, it will use the default value, like this:

def greet(name="World"):
    print(f"Hello, {name}!")

greet("Alice")

This will output:

Hello, Alice!

Try it yourself!

Keyword Arguments¶

We can more flexibly use functions by telling the function what we want to use as input when we call that function.

Let's imagine a scenario where we have a "describe_pet" function that takes two parameters: "animal_type" and "pet_name", the function might look like this:

def describe_pet(animal_type, pet_name):
    print(f"I have a {animal_type} named {pet_name}.")

We can specify the inputs, or "arguments", when we call the function by setting them equal to the parameter names.

Parameters & Arguments

The parameter is the name we give to the input in the function definition, and the argument is the actual value we pass to the function.

Here is an example of specifying that I have a dog named Rufus:

describe_pet(animal_type="dog", pet_name="Rufus")

Note that when I specify the arguments (inputs), I can change the order and the function will work just fine:

describe_pet(pet_name="Django", animal_type="dog")

So, in the code below, I can define the function and use the function twice in a row, changing the order of the arguments:

def describe_pet(animal_type, pet_name):
    print(f"I have a {animal_type} named {pet_name}.")

describe_pet(animal_type="dog", pet_name="Sherlock")
describe_pet(pet_name="Watson", animal_type="cat")

This will output:

I have a dog named Sherlock. I have a cat named Watson.

Exercises¶

Define a Function: Write a function called square that takes a number as a parameter and returns its square.
Solution
```
def square(number):
    return number * number

result = square(5)
print(result)
```
Call a Function: Write a function called multiply that takes two numbers as parameters and returns their product. Call the function with different arguments and print the results.
Solution
```
def multiply(a, b):
    return a * b

result1 = multiply(3, 4)
result2 = multiply(5, 2)
print(result1)
print(result2)
```
Default Parameters: Write a function called greet_user that takes a name as a parameter and prints a greeting message. If no name is provided, it should use "User" as the default name.
Solution
```
def greet_user(name="User"):
    print(f"Hello, {name}!")

greet_user("Alice")
greet_user()
```

Keyword Arguments: Write a function called make_sandwich that takes a list of ingredients and prints a message describing the sandwich. Call the function using keyword arguments to specify the ingredients in different orders.

Solution

def make_sandwich(ingredients):
    print("Sandwich with:")
    for ingredient in ingredients:
        print(f"- {ingredient}")

make_sandwich(ingredients=["bread", "cheese", "tomato"])
make_sandwich(ingredients=["tomato", "bread", "cheese"])

Reflect¶

Think about how functions can help you organize your code and make it more reusable. What are some real-world scenarios where you might use functions?

Review¶

In this step, we learned about functions in Python. Here's a quick recap:

Defining Functions: Use the def keyword to define a function.
Calling Functions: Use the function name followed by parentheses to call a function.
Return Statement: Use the return statement to return a value from a function.
Default Parameters: Define default values for parameters in a function.
Keyword Arguments: Specify arguments using parameter names when calling a function.

Understanding these concepts is essential for writing organized and reusable code in Python.