Python：我有一個好的語法嗎？

Question

我是新來編程，並開始學習Python.I做了一個簡單的計算器作爲練習和有問題與運行，因爲語法error.Could你告訴我，我犯的錯誤我的代碼：

while True: 
    print("Options:") 
    print("Enter 'add' to add two numbers") 
    print("Enter 'substract' to substract two numbers") 
    print("Enter 'multiply' to multiply two numbers") 
    print("Enter 'divide' to divide two numbers") 
    print("Enter 'quit' to end the program") 
    user_input = input(":") 

    if user_input == "quit": 
     break 

    elif user_input == "add": 
     ... 
    elif user_input == "substract": 
     ... 
    elif user_input == "multiply": 
     ... 
    elif user_input == "divide": 
     ... 
    else: 
     print("Unknown input") 

    elif user_input == "add": 
     num1 = float(input("Enter a number:")) 
     num2 = float(input("Enter another number:")) 
     result = str(num1 + num2) 
     print("The answer is:" + result) 

    elif user_input == "substract": 
     num1 = float(input("Enter a number:")) 
     num2 = float(input("Enter another number:")) 
     result = str(num1 - num2) 
     print("The answer is:" + result) 

    elif user_input == "multiply": 
     num1 = float(input("Enter a number:")) 
     num2 = float(input("Enter another number:")) 
     result = str(num1 * num2) 
     print("The answer is:" + result) 

    elif user_input == "divide": 
     num1 = float(input("Enter a number;")) 
     num2 = float(input("Enter another number:")) 
     result = str(num1/num2) 
     print("The answer is:" + result) 

感謝您的反饋！

Answer 1

因爲你的第二個ELIF語句是在else語句之後。

而且我添加了一個try和execpt塊的例子來處理ZeroDivisionError

while True: 
    print("Options:") 
    print("Enter 'add' to add two numbers") 
    print("Enter 'substract' to substract two numbers") 
    print("Enter 'multiply' to multiply two numbers") 
    print("Enter 'divide' to divide two numbers") 
    print("Enter 'quit' to end the program") 
    user_input = input(":") 

    if user_input == "quit": 
     break 
    elif user_input == "add": 
     num1 = float(input("Enter a number:")) 
     num2 = float(input("Enter another number:")) 
     result = str(num1 + num2) 
     print("The answer is:" + result) 

    elif user_input == "substract": 
     num1 = float(input("Enter a number:")) 
     num2 = float(input("Enter another number:")) 
     result = str(num1 - num2) 
     print("The answer is:" + result) 

    elif user_input == "multiply": 
     num1 = float(input("Enter a number:")) 
     num2 = float(input("Enter another number:")) 
     result = str(num1 * num2) 
     print("The answer is:" + result) 

    elif user_input == "divide": 
     num1 = float(input("Enter a number;")) 
     num2 = float(input("Enter another number:")) 
     # Example of a Try/Catch block to avoid ZeroDivisionError 
     try: 
      result = str(num1/num2) 
      print("The answer is:" + result) 
     except ZeroDivisionError: 
      print("Can't divide by 0") 
    else: 
     print("Unknown input")