19. 関数の定義と呼び出し

# 関数なし - 繰り返しのコード
length1 = 5
width1 = 3
area1 = length1 * width1
print(f"Area 1: {area1}")
 
length2 = 8
width2 = 4
area2 = length2 * width2
print(f"Area 2: {area2}")
 
length3 = 10
width3 = 6
area3 = length3 * width3
print(f"Area 3: {area3}")

Area 1: 15
Area 2: 32
Area 3: 60

def function_name():
    # 関数が呼び出されたときに実行されるコードブロック
    statement1
    statement2
    # ... さらに文が続く

def greet():
    print("Hello!")
    print("Welcome to Python functions.")
 
# Call the function
greet()

Hello!
Welcome to Python functions.

# 良い関数名
def calculate_total():
    pass
 
def get_user_age():
    pass
 
def display_menu():
    pass
 
# 良くない関数名（ただし文法的には正しい）
def x():  # 説明的ではない
    pass
 
def CalculateTotal():  # 小文字を使うべき
    pass
 
def calc():  # 省略しすぎ
    pass

def check_temperature():
    temperature = 72
    if temperature > 75:
        print("It's warm.")
    elif temperature > 60:
        print("It's comfortable.")
    else:
        print("It's cool.")
 
check_temperature()

It's comfortable.

def morning_greeting():
    print("Good morning!")
 
def evening_greeting():
    print("Good evening!")
 
# Call each function
morning_greeting()
evening_greeting()

Good morning!
Good evening!

# WARNING: This will cause a NameError - for demonstration only
# PROBLEM: Function called before it's defined
say_hello()  # NameError: name 'say_hello' is not defined
 
def say_hello():
    print("Hello!")

# Correct: Define first
def say_hello():
    print("Hello!")
 
# Then call
say_hello()

Hello!

def first_function():
    print("First function")
    second_function()  # これは問題ありません - 実行時に呼び出されます
 
def second_function():
    print("Second function")
 
# 最初の関数を呼び出す前に、両方の関数が定義されています
first_function()

First function
Second function

def create_message():
    message = "This is local"
    print(message)
 
create_message()
 
# This would cause an error:
# print(message)  # NameError: name 'message' is not defined

This is local

def future_feature():
    pass  # TODO: 後でこれを実装する
 
# 関数は存在し呼び出せますが、何もしません
future_feature()  # Runs without error, does nothing

def greet(name):  # 'name' はパラメータ
    print(f"Hello, {name}!")
 
greet("Alice")  # "Alice" は引数

Hello, Alice!

def greet_person(name):
    print(f"Hello, {name}!")
    print("Nice to meet you.")
 
# Call with different arguments
greet_person("Alice")
print()  # Blank line for readability
greet_person("Bob")

Hello, Alice!
Nice to meet you.
 
Hello, Bob!
Nice to meet you.

def calculate_rectangle_area(length, width):
    area = length * width
    print(f"A rectangle with length {length} and width {width}")
    print(f"has an area of {area} square units.")
 
calculate_rectangle_area(5, 3)
print()
calculate_rectangle_area(10, 7)

A rectangle with length 5 and width 3
has an area of 15 square units.
 
A rectangle with length 10 and width 7
has an area of 70 square units.

def describe_pet(animal_type, pet_name):
    print(f"I have a {animal_type}.")
    print(f"My {animal_type}'s name is {pet_name}.")
 
describe_pet("dog", "Buddy")
print()
describe_pet("cat", "Whiskers")

I have a dog.
My dog's name is Buddy.
 
I have a cat.
My cat's name is Whiskers.

def describe_pet(animal_type, pet_name):
    print(f"I have a {animal_type}.")
    print(f"My {animal_type}'s name is {pet_name}.")
 
# Arguments in wrong order
describe_pet("Buddy", "dog")

I have a Buddy.
My Buddy's name is dog.

def describe_pet(animal_type, pet_name):
    print(f"I have a {animal_type}.")
    print(f"My {animal_type}'s name is {pet_name}.")
 
# Using keyword arguments - order doesn't matter
describe_pet(animal_type="dog", pet_name="Buddy")
print()
describe_pet(pet_name="Whiskers", animal_type="cat")

I have a dog.
My dog's name is Buddy.
 
I have a cat.
My cat's name is Whiskers.

def create_profile(username, email, age):
    print(f"Username: {username}")
    print(f"Email: {email}")
    print(f"Age: {age}")
 
# Mixing positional and keyword arguments
create_profile("alice123", email="alice@example.com", age=25)

Username: alice123
Email: alice@example.com
Age: 25

# WARNING: This will cause a SyntaxError - for demonstration only
# PROBLEM: Positional argument after keyword argument
# create_profile(username="alice123", "alice@example.com", 25)
# SyntaxError: positional argument follows keyword argument

def add_numbers(a, b):
    result = a + b
    print(f"{a} + {b} = {result}")
 
add_numbers(5, 3)  # 正しい: 2つのパラメータに対して2つの引数

5 + 3 = 8

# WARNING: These will cause TypeErrors - for demonstration only
 
# PROBLEM: Too few arguments
# add_numbers(5)
# TypeError: add_numbers() missing 1 required positional argument: 'b'
 
# PROBLEM: Too many arguments
# add_numbers(5, 3, 2)
# TypeError: add_numbers() takes 2 positional arguments but 3 were given

def display_total(price, quantity):
    total = price * quantity
    print(f"Total cost: ${total:.2f}")
 
# Using expressions as arguments
base_price = 10
display_total(base_price * 1.1, 5)  # Price with 10% markup
display_total(15 + 5, 3 * 2)        # Both arguments are expressions

Total cost: $55.00
Total cost: $120.00

def calculate_area(length, width):
    return length * width
 
def display_room_info(room_name, length, width):
    area = calculate_area(length, width)
    print(f"Room: {room_name}")
    print(f"Dimensions: {length} x {width}")
    print(f"Area: {area} square feet")
 
display_room_info("Living Room", 15, 12)

Room: Living Room
Dimensions: 15 x 12
Area: 180 square feet

def celsius_to_fahrenheit(celsius):
    return (celsius * 9/5) + 32
 
def format_temperature(fahrenheit):
    return f"{fahrenheit:.1f}°F"
 
def display_temperature_conversion(celsius):
    fahrenheit = celsius_to_fahrenheit(celsius)
    formatted = format_temperature(fahrenheit)
    print(f"{celsius}°C equals {formatted}")
 
# Use the complete conversion system
display_temperature_conversion(25)
display_temperature_conversion(0)
display_temperature_conversion(100)

25°C equals 77.0°F
0°C equals 32.0°F
100°C equals 212.0°F

def add_numbers(a, b):
    result = a + b
    return result
 
# Capture the returned value
sum_value = add_numbers(5, 3)
print(f"The sum is: {sum_value}")

The sum is: 8

def multiply(a, b):
    return a * b
 
result = multiply(4, 7)
print(f"4 × 7 = {result}")

4 × 7 = 28

def calculate_discount(price, discount_percent):
    discount_amount = price * (discount_percent / 100)
    return discount_amount
 
original_price = 100
discount = calculate_discount(original_price, 20)
 
# Use the returned value in calculations
final_price = original_price - discount
print(f"Original price: ${original_price:.2f}")
print(f"Discount: ${discount:.2f}")
print(f"Final price: ${final_price:.2f}")

Original price: $100.00
Discount: $20.00
Final price: $80.00

def check_age(age):
    if age < 18:
        return "Minor"
    # This line only runs if age >= 18
    return "Adult"
 
print(check_age(15))
print(check_age(25))

Minor
Adult

def process_number(n):
    if n < 0:
        return "Negative"
    print("This line runs for non-negative numbers")
    if n == 0:
        return "Zero"
    print("This line runs for positive numbers")
    return "Positive"
 
print(process_number(-5))
print()
print(process_number(0))
print()
print(process_number(10))

Negative
 
This line runs for non-negative numbers
Zero
 
This line runs for non-negative numbers
This line runs for positive numbers
Positive

def greet(name):
    print(f"Hello, {name}!")
    # return 文はありません
 
result = greet("Alice")
print(f"The function returned: {result}")

Hello, Alice!
The function returned: None

def process_data(data):
    if not data:
        return  # 早期終了、None を返す
    print(f"Processing: {data}")
    return "Success"
 
result1 = process_data("")
result2 = process_data("some data")
 
print(f"Result 1: {result1}")
print(f"Result 2: {result2}")

Processing: some data
Result 1: None
Result 2: Success

def calculate_rectangle(length, width):
    area = length * width
    perimeter = 2 * (length + width)
    return area, perimeter
 
# Unpack the returned tuple
rect_area, rect_perimeter = calculate_rectangle(5, 3)
print(f"Area: {rect_area}")
print(f"Perimeter: {rect_perimeter}")

Area: 15
Perimeter: 16

def get_student_info():
    name = "Alice"
    age = 20
    grade = "A"
    return name, age, grade
 
# Capture as a tuple
student = get_student_info()
print(f"Student info: {student}")
print(f"Name: {student[0]}")

Student info: ('Alice', 20, 'A')
Name: Alice

def divide(a, b):
    if b == 0:
        return "Error: Division by zero"
    return a / b
 
result1 = divide(10, 2)
result2 = divide(10, 0)
 
print(f"10 / 2 = {result1}")
print(f"10 / 0 = {result2}")

10 / 2 = 5.0
10 / 0 = Error: Division by zero

def calculate_area(length, width):
    """Calculate the area of a rectangle.
    
    Takes the length and width of a rectangle and returns the area.
    """
    return length * width

def greet(name):
    """Print a personalized greeting."""
    print(f"Hello, {name}!")
 
# Access the docstring
print(greet.__doc__)

Print a personalized greeting.

def calculate_discount(price, discount_percent):
    """Calculate the discounted price.
    
    Takes an original price and a discount percentage, then returns
    the amount of discount that should be applied.
    
    Parameters:
    price (float): The original price before discount
    discount_percent (float): The discount percentage (0-100)
    
    Returns:
    float: The discount amount in the same currency as the price
    """
    return price * (discount_percent / 100)
 
# Use help() to see the full docstring
help(calculate_discount)

Help on function calculate_discount in module __main__:
 
calculate_discount(price, discount_percent)
    Calculate the discounted price.
    
    Takes an original price and a discount percentage, then returns
    the amount of discount that should be applied.
    
    Parameters:
    price (float): The original price before discount
    discount_percent (float): The discount percentage (0-100)
    
    Returns:
    float: The discount amount in the same currency as the price

def good_example():
    """This follows the convention."""
    pass
 
def also_valid():
    '''This works but is less common.'''
    pass

def add(a, b):
    """Return the sum of a and b."""
    return a + b

def process_order(order_id, items):
    """Process a customer order and update inventory.
    
    This function validates the order, checks inventory availability,
    calculates the total cost, and updates the inventory database.
    
    Parameters:
    order_id (str): Unique identifier for the order
    items (list): List of item dictionaries with 'product' and 'quantity'
    
    Returns:
    dict: Order summary with 'total', 'status', and 'confirmation_number'
    """
    # ここに関数の実装を書きます
    pass

def find_student(student_id, students):
    """Find a student by ID in a list of student records.
    
    Parameters:
    student_id (int): The unique ID number of the student to find
    students (list): List of student dictionaries, each containing 'id' and 'name'
    
    Returns:
    dict: The student dictionary if found, None if not found
    """
    for student in students:
        if student['id'] == student_id:
            return student
    return None

def safe_divide(a, b):
    """Divide two numbers with error handling.
    
    Parameters:
    a (float): The dividend
    b (float): The divisor
    
    Returns:
    float: The quotient if division is successful
    str: An error message if b is zero
    """
    if b == 0:
        return "Error: Cannot divide by zero"
    return a / b

def example():
    """This is an example function."""
    pass
 
print(example.__doc__)

This is an example function.

def calculate_bmi(weight, height):
    """Calculate Body Mass Index.
    
    Parameters:
    weight (float): Weight in kilograms
    height (float): Height in meters
    
    Returns:
    float: BMI value
    """
    return weight / (height ** 2)
 
help(calculate_bmi)

Help on function calculate_bmi in module __main__:
 
calculate_bmi(weight, height)
    Calculate Body Mass Index.
    
    Parameters:
    weight (float): Weight in kilograms
    height (float): Height in meters
    
    Returns:
    float: BMI value

def calculate_grade(score, total):
    """Calculate the percentage grade from a score.
    
    Parameters:
    score (int): Points earned
    total (int): Total points possible
    
    Returns:
    float: The percentage grade (0-100)
    """
    # ゼロ除算を避ける
    if total == 0:
        return 0.0
    
    # 割合を計算し、小数点以下2桁に丸める
    percentage = (score / total) * 100
    return round(percentage, 2)