如何用Python编写一个简单的计算器

要编写一个简单的计算器，我们可以使用Python的基本数学运算和控制结构。以下是一个简单的计算器的实现，具有加法、减法、乘法和除法的功能。

def add(num1, num2):
    return num1 + num2

def subtract(num1, num2):
    return num1 - num2

def multiply(num1, num2):
    return num1 * num2

def divide(num1, num2):
    if num2 != 0:
        return num1 / num2
    else:
        return "Error: Cannot divide by zero"

def calculator():
    print("Welcome to the calculator!")

    while True:
        print("Please choose an operation:")
        print("1. Add")
        print("2. Subtract")
        print("3. Multiply")
        print("4. Divide")
        print("5. Quit")

        choice = input("Enter your choice (1-5): ")
        
        if choice == '1':
            num1 = float(input("Enter the first number: "))
            num2 = float(input("Enter the second number: "))
            result = add(num1, num2)
            print("Result:", result)
        elif choice == '2':
            num1 = float(input("Enter the first number: "))
            num2 = float(input("Enter the second number: "))
            result = subtract(num1, num2)
            print("Result:", result)
        elif choice == '3':
            num1 = float(input("Enter the first number: "))
            num2 = float(input("Enter the second number: "))
            result = multiply(num1, num2)
            print("Result:", result)
        elif choice == '4':
            num1 = float(input("Enter the first number: "))
            num2 = float(input("Enter the second number: "))
            result = divide(num1, num2)
            print("Result:", result)
        elif choice == '5':
            print("Thank you for using the calculator!")
            break
        else:
            print("Invalid choice. Please try again.")

calculator()

上面的代码定义了四个函数来执行加法、减法、乘法和除法的操作。calculator()函数是主函数，用于接收用户的选择并执行相应的操作。用户可以选择要执行的操作，然后输入两个数字，计算器将返回结果并打印出来。用户可以重复选择操作，直到选择退出。

以下是一个使用此计算器的示例对话：

Welcome to the calculator!
Please choose an operation:
1. Add
2. Subtract
3. Multiply
4. Divide
5. Quit
Enter your choice (1-5): 1
Enter the first number: 2
Enter the second number: 3
Result: 5.0
Please choose an operation:
1. Add
2. Subtract
3. Multiply
4. Divide
5. Quit
Enter your choice (1-5): 4
Enter the first number: 10
Enter the second number: 2
Result: 5.0
Please choose an operation:
1. Add
2. Subtract
3. Multiply
4. Divide
5. Quit
Enter your choice (1-5): 5
Thank you for using the calculator!

希望通过这个例子你能了解如何使用Python编写一个简单的计算器。你可以根据需要扩展这个计算器，添加更多的操作和功能。