Python 函数在异常处理后不会终止

Question

如果我可以问：

即使在异常处理例程之后，我的 python 代码也不会终止。

这是代码：

import numpy as np

def calculate(num_list):
    try:
        num_array = np.array(num_list)
        num_array = np.reshape(num_array, (3, 3))
        # If the number of elements in num_list
        # is less than 9, np.reshape will return a
        # ValueError

    except ValueError:
        print("List must contain nine numbers.")

    # The problem is that after catching error with  
    # except ValueError:, the function continues 
    # and runs the three lines below.
    # And so, since num_array is not a valid input, I get
    # an axis value error.

    mean_list.append(np.mean(num_array, axis=0).tolist())
    mean_list.append(np.mean(num_array, axis=1).tolist())
    mean_list.append(np.mean(num_array).tolist())

我已经能够通过使用解决这个问题：

sys.stop() # After the print statement # 

或者在 mean_list.append 代码之前添加一个 if 语句

if len(np.array(num_list)) >= 9:

但是，我确定我的异常处理有问题。 如果有人能解释我遗漏了什么，将不胜感激。

非常感谢。 欣赏它。

Answer 1

您只捕获异常以记录一些信息，但希望异常传播回调用者。 所以只需再加注。

import numpy as np

def calculate(num_list):
    try:
        num_array = np.array(num_list)
        num_array = np.reshape(num_array, (3, 3))
        # If the number of elements in num_list
        # is less than 9, np.reshape will return a
        # ValueError

    except ValueError:
        print("List must contain nine numbers.")
        raise

        # or return an error (and return True otherwise)
        # return False
        # or convert to a different exception
        # raise MyAppError("Calculation Failed")
        # or just change the message (and probably not print anything)
        # raise ValueError("List must contain nine numbers.")
        # or fix the problem
        # num_array = my_default_array


    mean_list.append(np.mean(num_array, axis=0).tolist())
    mean_list.append(np.mean(num_array, axis=1).tolist())
    mean_list.append(np.mean(num_array).tolist())

捕获异常后，您有多种选择。 也许问题可以解决，程序可以继续。 也许您想将异常转换为另一种异常类型。 也许您想将该异常转换为错误返回值。 默认情况下，python 假定您只想在 try/except 块的末尾继续执行。

Answer 2

except块被编译except您可以使用return退出函数

import numpy as np

def calculate(num_list):
    try:
        num_array = np.array(num_list)
        num_array = np.reshape(num_array, (3, 3))
        # If the number of elements in num_list
        # is less than 9, np.reshape will return a
        # ValueError

    except ValueError:
        print("List must contain nine numbers.")
        return

    # The problem is that after catching error with  
    # except ValueError:, the function continues 
    # and runs the three lines below.
    # And so, since num_array is not a valid input, I get
    # an axis value error.

    mean_list.append(np.mean(num_array, axis=0).tolist())
    mean_list.append(np.mean(num_array, axis=1).tolist())
    mean_list.append(np.mean(num_array).tolist())