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python - 我的 python 代码做了它打算做的事情，但是中断/继续使用 try/catch 块？

问题描述

#A 0-50 Units is multiplied by $0.59 (multiply by 0.59)
#B Up to 150 Units (minus 50 and multiply remaning by 0.65)
#C Greater than 150 Units(minus 150(first 150 = $94.50) and multiply remaining by 0.68)
#D All Residential charges are fixed @ $13.00(always add $13)
                
print ("      *        SKELEC Electricity Bill Calculator        *       ")

def main():
    
    while True:
        try:
            prev_month = float(input("Enter the meter reading for the previous month\n"))
            break
        except ValueError:
            print("Invalid value entered. Please try again.")
            continue
        
    if prev_month < 0:
            print("Please enter a valid reading.")
            main()
            
    while True:
        try:
            pres_month = float(input("Enter the meter reading for the current month\n"))
            break
        except ValueError:
            print("Invalid value entered. Please try again.")
            continue
        
    if pres_month < 0:
            print("Please enter a valid reading.")
            main()

    if pres_month < prev_month:
            print("Present month value is lower than previous month value")
            main()

    units_kwh = pres_month - prev_month #Variable for the subtraction of present month and previous month
    
    print("Usage = ", units_kwh,"kw/h")

    if units_kwh <= 50: #Argument for 0-50 kwh units
        Energy_charge = units_kwh * 0.59
        print("Your charge for the month is, $", Energy_charge)

    elif units_kwh > 50 and units_kwh <= 150: #Argument for units up to 150kwh
            units_fifty = units_kwh - 50
            Energy_charge = (units_fifty * 0.65 + 29.50) + 13.00
            print("Your charge for the month is, $", Energy_charge)


    elif units_kwh > 150: #Argument for units over 150kwh
            Energy_charge = ((units_kwh - 150) * 0.68 + 94.50) + 13.00
            print("Your charge for the month is, $", Energy_charge)
            
    print("Residential Charge of $13.00 added")

            
main()

一切正常，但如果一开始输入了不正确的值（例如字符），一旦给出最终结果，代码就会不必要地循环。我尝试将 try/catch 块移到循环之外，仔细检查我的条件语句并校对以查看代码如何以这种方式循环。我确信问题出在 try/catch 块中，但我对使用 Python 编码还很陌生，所以我不确定如何解决这个问题？

标签： pythonexceptiontry-catch

解决方案

您可以进行一些更改以改进代码：

  • 如果用户输入负数，则引发异常
  • 为条件添加一个外while循环pres_month < prev_month

试试这个代码：

def main():
    
    while True:  # pres_month < prev_month
    
        while True:
            try:
                prev_month = float(input("Enter the meter reading for the previous month\n"))
                if prev_month < 0: raise ValueError()
                break
            except ValueError:
                print("Invalid value entered. Please try again.")
            
        while True:
            try:
                pres_month = float(input("Enter the meter reading for the current month\n"))
                if pres_month < 0: raise ValueError()
                break
            except ValueError:
                print("Invalid value entered. Please try again.")
            
        if pres_month < prev_month:
                print("Present month value is lower than previous month value")
        else:
                break  # data is valid

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