异常问题

Question

告诉我有一个ValueError异常，请注意。困惑为什么我继续收到错误消息。

def readHourlyRate():
    try:
       rate = float(input('Hourly Rate:$')) 
       if rate < 20:
           print("Must be atleast $20.00/ hour")
    except ValueError:
        print("\nInvalid Hourly Rate, must be atleast $20.00/hour.")
        return rate

Answer 1

使用此工作示例：

def readHourlyRate():
    try:
        rate = float(input('Hourly Rate:$'))
        if rate < 20:
            print("Must be atleast $20.00/ hour")
    except ValueError:
        print("\nInvalid Hourly Rate, must be atleast $20.00/hour.")
        return rate

readHourlyRate()

然后将字符串作为输入，这就是您得到的回溯：

Traceback (most recent call last):
  File "C:/[...].py", line 3, in readHourlyRate
    rate = float(input('Hourly Rate:$'))
ValueError: could not convert string to float: 'sdfsdf'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:/[...].py", line 10, in <module>
    readHourlyRate()
  File "C:/[...].py", line 8, in readHourlyRate
    return rate
UnboundLocalError: local variable 'rate' referenced before assignment

通过仔细阅读它，我们可以看到在处理由无效输入引发的ValueError异常期间，由于我们试图返回rate变量，引发了另一个未处理的异常。 但是，从未声明或分配此变量，因为在我们尝试这样做时引发了ValueError。

根据您希望程序执行的操作，然后可以在except块中分配一个默认值，如下所示：

except ValueError:
print("Invalid Hourly Rate, must be atleast $20.00/hour.")
print("Returning default value 20")
return 20

或者只是让错误传播

Answer 2

尝试一下：

def readHourlyRate():
    rate = input('Hourly Rate:$')
    try:
       if float(rate) < 20:
           print("Must be atleast $20.00/ hour")
    except Exception as e:
        print("\nInvalid Hourly Rate, must be atleast $20.00/hour.")
        return rate

readHourlyRate()

Answer 3

将代码更改为以下内容：-

GaussianBlur(im, tempIm, Size(9, 9), 1, 1, BORDER_REFLECT);
findContours(tempIm, contours, hierarchy, RETR_TREE, CHAIN_APPROX_TC89_KCOS);