try
语句有一个可选finally子句,用于定义在所有情况下都必须执行的finally操作
try:
raise KeyboardInterrupt
finally:
print('Goodbye, world!')
Goodbye, world!
KeyboardInterrupt
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
如果存在finally
子句,则该finally
子句将作为try
语句完成之前的最后一项任务执行。finally
无论该try
语句是否产生异常,该子句都会运行。
以下几点讨论了发生异常时更复杂的情况:
try
子句期间发生异常,则该异常可以由except
子句处理。如果该异常未由except
子句处理,finally
则在执行该子句后将重新引发该异常。
except
or else
子句期间可能会发生异常。同样,在finally
执行该子句之后,将重新引发异常。
try
语句到达break
,continue
或return
语句时,finally
条款将在<try or else or except的>break
,continue
或return
语句之前执行。
finally
子句包含一条return
语句,则该finally
子句的return
语句将在<try or else or except的>子句中的return语句之前执行,所以事实上执行了的是finally的return,而不是在<try or else or except>中执行return
语句。
案例1.
>>> def bool_return():
... try:
... return True
... finally:
... return False
...
>>> bool_return()
False
案例2.
def bool_return():
try:
raise Exception
except Exception:
return True
finally:
return False
print(bool_return())
False
案例3.
>>> def divide(x, y):
... try:
... result = x / y
... except ZeroDivisionError:
... print("division by zero!")
... else:
... print("result is", result)
... finally:
... print("executing finally clause")
...
>>> divide(2, 1)
result is 2.0
executing finally clause
>>> divide(2, 0)
division by zero!
executing finally clause
>>> divide("2", "1")
executing finally clause
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in divide
TypeError: unsupported operand type(s) for /: 'str' and 'str'