如何输入字符串来运行？

Question

以下是我收到的作业说明：

4) 在 Mylib 中添加如下函数

scalc(p1)
p1 will be a string like this "N1, N2, operator"
examples
scalc("20,30,*")
the result will be 600

scalc("50,20,+")
the result will be 70

scalc("50,20,-")
the result will be 30

scalc("60,20,/")
the result will be 30

使用字符串函数从输入字符串中解析第一个数字、第二个数字和运算符。 使用前面的函数（加、减、除和乘）进行计算。

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这是我的尝试，但不起作用。我有 add() sub() mult() div() 函数，我只是不在这里展示它们。

我知道这很简单，可能与我调用函数 scalc(p1) 的位置有关。这样做的正确方法是什么？

def scalc(p1):
    astring = p1.split(",")
    num1 = float(astring[0])
    num2 = float(astring[1])
    if astring[3] == "+":
        add()
    elif astring[3] == "-":
        sub()
    elif astring[3] == "*":
        mult()
    elif astring[3] == "/":
        div()
    return num1, num2

p1 = input("Enter two numbers and an operator, each separated by a comma: ")
scalc(p1)

编辑：这是答案。我没有将参数传递给我的函数。通过将 num1 和 num2 添加到我的算术函数的每个实例中，它们能够接收新的变量值。

#Define the main program function
def main():
    #Define input function
    def float_input(msg):
        while True:
            try:
                return float(input(msg))
            except ValueError:
                print("You must enter a number!")
            else:
                break
    #Declare variables        
    rangeLower = float_input("Enter your Lower range: ")
    rangeHigher = float_input("Enter your Higher range: ")
    num1 = float_input("Enter your First number: ")
    num2 = float_input("Enter your Second number: ")

    #Define formula functions
    def add(num1, num2):
        sum = num1 + num2
        print("The Result of",num1,"+",num2,"=", sum)

    def sub(num1, num2): 
        diff = num1 - num2
        print("The Result of",num1,"-",num2,"=", diff)

    def mult(num1, num2):
        product = num1 * num2
        print("The Result of",num1,"*",num2,"=", product)

    def div(num1, num2):
        if num2 == 0:
            print("The Result of",num1,"/",num2,"= You cannot divide by Zero")
        else:
            quotient = num1 / num2
            print("The Result of",num1,"/",num2,"=", quotient)

    #If-else
    if num1 < rangeLower or num1 > rangeHigher or num2 < rangeLower or num2 > rangeHigher:
        print("The input values are outside the input ranges.")
        print("Please check the number and try again.")
        print("Thanks for using our calculator")
    else:
        #Call functions
        add(num1, num2)
        sub(num1, num2)
        mult(num1, num2)
        div(num1, num2)
        print("Thanks for using this calculator!")

    def scalc(p1):
        astring = p1.split(",")
        num1 = float(astring[0])
        num2 = float(astring[1])
        if astring[2] == "+":
            add(num1, num2)
        elif astring[2] == "-":
            sub(num1, num2)
        elif astring[2] == "*":
            mult(num1, num2)
        elif astring[2] == "/":
            div(num1, num2)
        return num1, num2

    p1 = input("Enter two numbers and an operator, each separated by a comma: ")
    scalc(p1)

Answer 1

这样做。有几个错误。首先，在 Python 中，您从 0 开始计数，因此您想使用 astring[2] 而不是 astring[3]。您还需要返回一个值：

def scalc(p1):
    astring = p1.split(",")
    print(astring)
    num1 = float(astring[0])
    num2 = float(astring[1])
    if astring[2] == "+":
        add(num1,num2)
    elif astring[2] == "-":
       sub(num1,num2)
    elif astring[2] == "*":
        mult(num1,num2)
    elif astring[2] == "/":
        div(num1,num2)
    return value

p1 = input("Enter two numbers and an operator, each separated by a comma: ")
scalc(p1)

例子：

input: "20,30,+"

Out[2]: 50.0