Writes a Python code for a simple calculator app that can perform addition, subtraction, multiplication, and division. It should use functions for each operation and handle exceptions for division by zero.
user
Here's a simple Python code for a calculator app that performs addition, subtraction, multiplication, and division, with exception handling for division by zero:

```python
def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

def multiply(x, y):
    return x * y

def divide(x, y):
    try:
        return x / y
    except ZeroDivisionError:
        return "Error: Division by zero is not allowed."

def main():
    print("Select operation:")
    print("1. Add")
    print("2. Subtract")
    print("3. Multiply")
    print("4. Divide")
    
    choice = input("Enter choice (1/2/3/4): ")
    
    if choice in ('1', '2', '3', '4'):
        num1 = float(input("Enter first number: "))
        num2 = float(input("Enter second number: "))
        
        if choice == '1':
            print("Result:", add(num1, num2))
        elif choice == '2':
            print("Result:", subtract(num1, num2))
        elif choice == '3':
            print("Result:", multiply(num1, num2))
        elif choice == '4':
            result = divide(num1, num2)
            print("Result:", result)
    else:
        print("Invalid input")

if __name__ == "__main__":
    main()
```

This code defines functions for each arithmetic operation and uses a `try-except` block in the `divide` function to handle division by zero. The `main` function handles user input and calls the appropriate function based on the user's choice.
assistant
Ensure the input is properly converted to a float and handle any conversion errors.
user
Sure! Here's the updated Python code for the calculator app that handles input conversion errors and ensures proper conversion to `float`:

```python
def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

def multiply(x, y):
    return x * y

def divide(x, y):
    try:
        return x / y
    except ZeroDivisionError:
        return "Error: Division by zero is not allowed."

def main():
    print("Select operation:")
    print("1. Add")
    print("2. Subtract")
    print("3. Multiply")
    print("4. Divide")
    
    choice = input("Enter choice (1/2/3/4): ")
    
    if choice in ('1', '2', '3', '4'):
        try:
            num1 = float(input("Enter first number: "))
            num2 = float(input("Enter second number: "))
        except ValueError:
            print("Error: Invalid input. Please enter numeric values.")
            return
        
        if choice == '1':
            print("Result:", add(num1, num2))
        elif choice == '2':
            print("Result:", subtract(num1, num2))
        elif choice == '3':
            print("Result:", multiply(num1, num2))
        elif choice == '4':
            result = divide(num1, num2)
            print("Result:", result)
    else:
        print("Invalid input")

if __name__ == "__main__":
    main()
```

In this updated version, the `try-except` block is used to catch `ValueError` exceptions that occur when the input cannot be converted to a `float`. If a conversion error occurs, an error message is printed, and the program returns without performing any calculations.
assistant
Add a function to clear the screen before showing the menu. Use `os.system('clear')` for Linux and `os.system('cls')` for Windows.
user
Sure! Here's the updated Python code for the calculator app that includes a function to clear the screen before showing the menu. This function will use `os.system('clear')` for Linux and `os.system('cls')` for Windows:

```python
import os

def clear_screen():
    if os.name == 'nt':  # Windows
        os.system('cls')
    else:  # Linux and other Unix systems
        os.system('clear')

def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

def multiply(x, y):
    return x * y

def divide(x, y):
    try:
        return x / y
    except ZeroDivisionError:
        return "Error: Division by zero is not allowed."

def main():
    while True:
        clear_screen()
        print("Select operation:")
        print("1. Add")
        print("2. Subtract")
        print("3. Multiply")
        print("4. Divide")
        print("5. Exit")
        
        choice = input("Enter choice (1/2/3/4/5): ")
        
        if choice == '5':
            print("Exiting the calculator.")
            break
        
        if choice in ('1', '2', '3', '4'):
            try:
                num1 = float(input("Enter first number: "))
                num2 = float(input("Enter second number: "))
            except ValueError:
                print("Error: Invalid input. Please enter numeric values.")
                input("Press Enter to continue...")
                continue
            
            if choice == '1':
                print("Result:", add(num1, num2))
            elif choice == '2':
                print("Result:", subtract(num1, num2))
            elif choice == '3':
                print("Result:", multiply(num1, num2))
            elif choice == '4':
                result = divide(num1, num2)
                print("Result:", result)
        else:
            print("Invalid input")
        
        input("Press Enter to continue...")

if __name__ == "__main__":
    main()
```

### Explanation:
1. **`clear_screen` Function**: This function checks the operating system using `os.name`. If it's `nt` (Windows), it uses `os.system('cls')` to clear the screen. For other systems (like Linux and macOS), it uses `os.system('clear')`.
2. **Main Loop**: The `main` function now includes a `while True` loop to keep the calculator running until the user chooses to exit.
3. **Exit Option**: Added an option `5` to exit the calculator. When the user selects this option, the loop breaks and the program exits.
4. **Continuation**: After each operation, the user is prompted to press Enter to continue, which keeps the result visible before clearing the screen and showing the menu again.

This ensures a clean and user-friendly interface for the calculator app.
assistant