Python对象Exception类异常捕捉
jiangwei0512 人气:0异常对象
Python中遇到错误后，会引发异常。
Python中使用异常对象来表示异常情况。
如果异常对象未被处理或者捕捉，程序就会用所谓的回溯（traceback）来终止执行。
下面是一个例子：
def func1():
raise Exception
if __name__ == "__main__":
func1()执行之后报错：
(venv) E:\Codes\python_everything\begining-python\src\08>list8-2.py
Traceback (most recent call last):
File "E:\Codes\python_everything\begining-python\src\08\list8-2.py", line 19, in <module>
func1()
File "E:\Codes\python_everything\begining-python\src\08\list8-2.py", line 15, in func1
raise Exception
Exception异常有不同的类型，Exception是基础类，下面还有各种子类：
+-- Exception
+-- StopIteration
+-- StandardError
| +-- BufferError
| +-- ArithmeticError
| | +-- FloatingPointError
| | +-- OverflowError
| | +-- ZeroDivisionError
| +-- AssertionError
| +-- AttributeError
| +-- EnvironmentError
| | +-- IOError
| | +-- OSError
| | +-- WindowsError (Windows)
| | +-- VMSError (VMS)
| +-- EOFError
| +-- ImportError
| +-- LookupError
| | +-- IndexError
| | +-- KeyError
| +-- MemoryError
| +-- NameError
| | +-- UnboundLocalError
| +-- ReferenceError
| +-- RuntimeError
| | +-- NotImplementedError
| +-- SyntaxError
| | +-- IndentationError
| | +-- TabError
| +-- SystemError
| +-- TypeError
| +-- ValueError
| +-- UnicodeError
| +-- UnicodeDecodeError
| +-- UnicodeEncodeError
| +-- UnicodeTranslateError还可以通过继承Exception来实现自己的类：
class SomeError(Exception): pass
def func2():
raise SomeError
if __name__ == "__main__":
func2()异常捕捉
异常可以被捕捉，需要使用try...except...语句：
class SomeError(Exception): pass
def func2():
raise SomeError
if __name__ == "__main__":
try:
func2()
except SomeError:
print("Some error happened")这里捕捉到了参数，所以就不会回溯：
(venv) E:\Codes\python_everything\begining-python\src\08>list8-3.py Some error happened
但是如果是其它的异常：
def func1():
raise Exception
class SomeError(Exception): pass
def func2():
raise SomeError
if __name__ == "__main__":
try:
func1()
except SomeError:
print("Some error happened")这里的Exception就没有被捕获，所以还是会回溯：
(venv) E:\Codes\python_everything\begining-python\src\08>list8-3.py
Traceback (most recent call last):
File "E:\Codes\python_everything\begining-python\src\08\list8-3.py", line 27, in <module>
func1()
File "E:\Codes\python_everything\begining-python\src\08\list8-3.py", line 15, in func1
raise Exception
Exception如果没有出现异常，则会继续往下执行，但是这里可以有else语句来执行没有异常时可以执行的语句，使整个逻辑更通顺：
if __name__ == "__main__":
try:
print("No exception")
except SomeError:
print("Some error happened")
else:
print("No error happened")结果如下：
(venv) E:\Codes\python_everything\begining-python\src\08>list8-3.py No exception No error happened
但是有时即使发生了无法捕捉的异常，也想要执行一些语句，这个时候就可以使用finally语句：
def func1():
raise Exception
class SomeError(Exception): pass
def func2():
raise SomeError
if __name__ == "__main__":
try:
func1()
except SomeError:
print("Some error happened")
else:
print("No error happened")
finally:
print("Do something")Python中更倾向于使用try...except...这样的语句来代替if...else..语句。
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