异常处理

抛出异常写法： raise  KeyError(obj)   # obj可以为字符串，数字，元祖，列表，字典等任意类型。

'''
异常处理格式
'''
try:
    pass
except KeyError  as e:
    print("key error..", e)
except IndexError as e:
    print("列表错误", e)
except Exception as e:
    print("未知错误,用在除上面两种情况外的所有错误", e)
else:
    print("一切正常（没有任何错误的时候执行这个）")
finally:
    print("不管出不出错，都会执行这个")

######
try:
    pass
except (KeyError,IndexError) as e:
    print("两种错误，同一种处理方式")
#####
try:
    pass
except Exception as e:
    print("抓所有错误，一般不在最开始使用")
####
'''
自定义异常
'''
class MyException(Exception):
    def __init__(self, msg):
        self.msg = msg
    def __str__(self):
        return "自己定义的异常"

try:
    raise MyException("我自定义的异常")
except MyException as e:
    print(e)

'''
输出结果：
一切正常（没有任何错误的时候执行这个）
不管出不出错，都会执行这个
自己定义的异常
'''

 ==异常树===

BaseException
 +-- SystemExit
 +-- KeyboardInterrupt
 +-- GeneratorExit
 +-- Exception
      +-- StopIteration
      +-- StopAsyncIteration
      +-- ArithmeticError
      |    +-- FloatingPointError
      |    +-- OverflowError
      |    +-- ZeroDivisionError
      +-- AssertionError
      +-- AttributeError
      +-- BufferError
      +-- EOFError
      +-- ImportError
      |    +-- ModuleNotFoundError
      +-- LookupError
      |    +-- IndexError
      |    +-- KeyError
      +-- MemoryError
      +-- NameError
      |    +-- UnboundLocalError
      +-- OSError
      |    +-- BlockingIOError
      |    +-- ChildProcessError
      |    +-- ConnectionError
      |    |    +-- BrokenPipeError
      |    |    +-- ConnectionAbortedError
      |    |    +-- ConnectionRefusedError
      |    |    +-- ConnectionResetError
      |    +-- FileExistsError
      |    +-- FileNotFoundError
      |    +-- InterruptedError
      |    +-- IsADirectoryError
      |    +-- NotADirectoryError
      |    +-- PermissionError
      |    +-- ProcessLookupError
      |    +-- TimeoutError
      +-- ReferenceError
      +-- RuntimeError
      |    +-- NotImplementedError
      |    +-- RecursionError
      +-- SyntaxError
      |    +-- IndentationError
      |         +-- TabError
      +-- SystemError
      +-- TypeError
      +-- ValueError
      |    +-- UnicodeError
      |         +-- UnicodeDecodeError
      |         +-- UnicodeEncodeError
      |         +-- UnicodeTranslateError
      +-- Warning
           +-- DeprecationWarning
           +-- PendingDeprecationWarning
           +-- RuntimeWarning
           +-- SyntaxWarning
           +-- UserWarning
           +-- FutureWarning
           +-- ImportWarning
           +-- UnicodeWarning
           +-- BytesWarning
           +-- ResourceWarning