异常

• 异常的种类

ArithmeticError
AssertionError
AttributeError
BaseException
BufferError
BytesWarning
DeprecationWarning
EnvironmentError
EOFError
Exception
FloatingPointError
FutureWarning
GeneratorExit
ImportError
ImportWarning
IndentationError
IndexError
IOError
KeyboardInterrupt
KeyError
LookupError
MemoryError
NameError
NotImplementedError
OSError
OverflowError
PendingDeprecationWarning
ReferenceError
RuntimeError
RuntimeWarning
StandardError
StopIteration
SyntaxError
SyntaxWarning
SystemError
SystemExit
TabError
TypeError
UnboundLocalError
UnicodeDecodeError
UnicodeEncodeError
UnicodeError
UnicodeTranslateError
UnicodeWarning
UserWarning
ValueError
Warning
ZeroDivisionError

•  语法结构

try:
    # 主代码块
    pass
except KeyError as e:
    # 异常时，执行该块
    pass
else:
    # 主代码块执行完并且无异常，执行该块
    pass
finally:
    # 无论异常与否，最终执行该块
    pass

•  主动抛出异常

try:
    raise Exception('错误了。。。')
except Exception as e:
    print(e)  #打印：错误了。。。

扩展： e是Exception的对象，print一个对象是先调用了对象的__str__方法，然后把返回的字符串打印

•  自定义异常

class MyException(Exception):
    def __init__(self, message):
        self.message = message

    def __str__(self):
        return self.message

try:
    raise MyException('出错了...')
except MyException as e:
    print(e)

•  断言：如果断言语句为真，代码继续执行，如果为假，则抛出AssertionError异常

assert True
print('True')
assert False    #抛出异常，之后的代码不会执行
print('False')