Python中的 Try、Except、else 和 finally

异常是在程序执行期间发生的事件。它也称为运行时错误。当该错误发生时， Python会在执行过程中生成一个可以处理的异常，从而避免您的程序中断。

例子：

Python3

a = 5
b = 0
print(a/b)

输出：

Traceback (most recent call last):
  File "/home/8a10be6ca075391a8b174e0987a3e7f5.py", line 3, in 
    print(a/b)
ZeroDivisionError: division by zero

在此代码中，系统无法将数字除以零，因此引发异常。

使用 try、except、else 和 finally 处理异常

• Try ：此块将测试发生的异常错误
• 除了：在这里您可以处理错误
• Else ：如果没有异常，则将执行此块
• finally ：无论是否生成异常，Finally 块总是被执行

句法：

try:
       # Some Code.... 

except:
       # optional block
       # Handling of exception (if required)

else:
       # execute if no exception

finally:
      # Some code .....(always executed)

让我们首先了解 try 和 except 是如何工作的——

• 执行第一个try子句，即try和except子句之间的代码。
• 如果没有异常，那么只有try子句会运行， except子句不会被执行。
• 如果发生任何异常，将跳过try子句并运行except子句。
• 如果发生任何异常，但代码中的except子句不处理它，则将其传递给外部try语句。如果异常未处理，则执行停止。
• 一条try语句可以有多个except子句。

示例：让我们尝试接受用户整数输入并在 except 块中抛出异常。

Python3

# Python code to illustrate
# working of try() 
def divide(x, y):
    try:
        # Floor Division : Gives only Fractional
        # Part as Answer
        result = x // y
        print("Yeah ! Your answer is :", result)
    except ZeroDivisionError:
        print("Sorry ! You are dividing by zero ")
   
# Look at parameters and note the working of Program
divide(3, 2)
divide(3, 0)

输出：

Yeah ! Your answer is : 1
Sorry ! You are dividing by zero 

其他条款

只有当 try 子句没有引发异常时，代码才会进入 else 块。

示例：只有在没有异常发生时才会执行 Else 块。

Python3

# Python code to illustrate
# working of try() 
def divide(x, y):
    try:
        # Floor Division : Gives only Fractional
        # Part as Answer
        result = x // y
    except ZeroDivisionError:
        print("Sorry ! You are dividing by zero ")
    else:
        print("Yeah ! Your answer is :", result)
   
# Look at parameters and note the working of Program
divide(3, 2)
divide(3, 0)

输出：

Yeah ! Your answer is : 1
Sorry ! You are dividing by zero

最后关键字

Python提供了一个关键字 finally，它总是在 try 和 except 块之后执行。 finally 块总是在 try 块正常终止后或 try 块由于某些异常终止后执行。

示例：让我们尝试在 except 块中抛出异常，最终将执行任一异常是否会生成

Python3

# Python code to illustrate
# working of try() 
def divide(x, y):
    try:
        # Floor Division : Gives only Fractional
        # Part as Answer
        result = x // y
    except ZeroDivisionError:
        print("Sorry ! You are dividing by zero ")
    else:
        print("Yeah ! Your answer is :", result)
    finally: 
        # this block is always executed  
        # regardless of exception generation. 
        print('This is always executed')  
 
# Look at parameters and note the working of Program
divide(3, 2)
divide(3, 0)

输出：

Yeah ! Your answer is : 1
This is always executed
Sorry ! You are dividing by zero 
This is always executed