LESSON 7: FUNCTIONS

🔹 A function is defined using the def keyword. The structure looks like this:

Python Code

def greet(): # function name

   print("Hello! This is my first function.")  # code block (indented)

greet() # To use the function (call it)

✅ Try It:

Open Google Colab, create a new notebook, and run the examples above in new code cells.

💡If you need to greet users in multiple places, instead of repeating print("Hello!") everywhere, just call greet().

🔹 A parameter is the placeholder name listed in a function’s definition (e.g., def greet(name): → name is a parameter).

🔹 Parameters are inputs to the function. 

🔹 An argument is the actual value passed to the function when it is called (e.g., greet("Ali") → "Ali" is the argument).

🔹 Return values are outputs the function sends back (e.g., def add(a, b): return a + b → a + b is returned)

Python Code

def greet(name):  # 'name' is a parameter

   print("Hello,", name)

greet("Ali")  # "Ali is an argument

Python Code

def add_numbers(a, b):

   return a + b  

# a + b is returned by the function and stored in result

result = add_numbers(5, 7) # Calling the function

print("Sum:", result)

✅ Try It:

Run the examples above in new code cells.

🧠 Quick Tip:

• print() shows something on the screen but does not return a value to use later.

• return gives back a value that you can store, modify, or print later.

🔹 Parameter → Name for expected input (like an empty box waiting to be filled).

🔹 Argument → Actual input you give to the box.
🔹 Return Value → The result the function hands back to you after doing something.

Python Code

# Defining the function (Parameter is 'name')

def greet(name):

   return "Hello, " + name

# Calling the function (Argument is 'Ali')

message = greet("Ali")

# 'Hello, Ali' is the return value

print(message)

✅ Try It:

Run the examples above in new code cells.

Python Code

def square(x):

   return x * x

result = square(4)

print("Square:", result)  # Output: Square: 16

✅ Try It:

Run the examples above in new code cells.

Python Code

def square(x):

   print(x * x)  # Just displays result, doesn’t give it back

square(5)  # Output: 25

✅ Try It:

Run the examples above in new code cells.

🔹 Scope: Where a variable can be used

🔹 2 types of variables:

(1) Local variable: Created inside a function. Can only be used there.

(2) Global variable: Created outside any function. Can be accessed anywhere.

Python Code

def show_local():

   x = 10  # local

   print("Inside:", x)

x = 5  # global

show_local()

print("Outside:", x)

✅ Try It:

Run the examples above in new code cells.

🔹 Changing a global variable inside a function:

Python Code

x = 10

def modify():

   global x

   x = 20

modify()

print(x)  # Output: 20

✅ Try It:

Run the examples above in new code cells.

Python Code

def multiply(a, b):

   return a * b

product = multiply(4, 5)

print("Product:", product)

✅ Try It:

Run the examples above in new code cells.

Python Code

def check_even(num):

   if num % 2 == 0:

       return "Even"

   else:

       return "Odd"

print(check_even(7))  # Output: Odd

✅ Try It:

Run the examples above in new code cells.

🧠 Answer these to test your understanding.

1. A function must always return a value. (True / False)

2. Which keyword is used to define a function?

a) func

b) def

c) function

3. What happens if you try to access a local variable outside the function?

4. What’s the difference between a parameter and an argument?

5. How is a local variable different from a global one?

🔧 Instructions:

1. Function to calculate area of a rectangle

✅ Define a function named calculate_area

✅ It should take two parameters: length and width

✅ It should return the area (length × width)

2. Function to find maximum of three numbers

✅ Define a function named find_max

✅ Accept three parameters

✅ Return the highest value using conditional logic or the built-in max() function

3. Function to convert celsius to fahrenheit

✅ Formula: F = C × 9/5 + 32

🔹 A function is a reusable block of code that performs a specific task.

🔹 Functions are defined using the def keyword.

🔹 Parameters are names listed in the function definition to accept inputs.

🔹 Arguments are actual values passed to a function when it is called.

🔹 The return statement sends a value back to the place where the function was called.

🔹 If no return is used, the function returns None by default.

🔹 Local variables exist only inside the function where they are created.

🔹 Global variables are accessible from anywhere in the program.

🔹 Functions help make code cleaner, easier to read, more organized, and more reusable.