Exceptions and exception handling

abnormal ：
         Compared with normal, abnormal phenomena are called anomalies , Encountered errors or BUG All are
         Supplement normal conditions （ Errors are not exceptions , Exceptions are not equivalent to errors , Exception refers to the software running , For some reason （ Improper use by users ） Program error caused by , The phenomenon that leads to software crash is called exception ）

         Abnormal consequences ： Cause the program to crash

Handling exceptions ：
         There are abnormal errors in tolerance , Ensure the normal operation of the program
         Processing mode ：try : - except: Sentence block         Exception trapping
    
          Code exception ： It does not affect the execution of the following code , You need to continue to execute the following code
         Format ：
        try:
                #   Code where exceptions can occur
        except:
               #   Handling exceptions

Custom exception ：
        finally keyword ： Code that must be executed （ Release resources 、io）

         If in a function , If return Post existence finally keyword , Then the code will not
         Go straight back to （ perform return）, But to perform finally Code block , Then execute the return （return）, all finally Will be in return Before execution

         Common abnormal ：
                import builtins
                dir(builtins)
             Abnormal inheritance relationship ：
                BaseException() The parent of all exceptions

                Exception() （BaseException() Subclasses of ） Is the parent of common exceptions

         Custom exception ：
             First create a class , Inherit Exception perhaps BaseException, It is recommended to use Exception class

class MyException(Exception):
    def __init__(self):
        Exception.__init__(self,msg)
def login(username,password):
    if username==None or username.strip()=='':
        # Throw an exception —— Use  raise keyword （ Custom throw exception ）
        raise MyException(" The username cannot be empty ")
    if password==None or password.strip()=='':
        #  Throw an exception —— Use  raise keyword （ Custom throw exception ）
        raise MyException(" The password cannot be empty ")
if __name__ == '__main__':
    try:
        #login(None,None)
        # Capture exception 
        login(None,None)
    except Exception as e:
        print(" Exception caught as >>>>",e)

'ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'Buffer
Error', 'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError', 'ConnectionRefusedError', 'C
onnectionResetError', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FileExi
stsError', 'FileNotFoundError', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'Imp
ortWarning', 'IndentationError', 'IndexError', 'InterruptedError', 'IsADirectoryError', 'KeyError', 'KeyboardInterrupt
', 'LookupError', 'MemoryError', 'ModuleNotFoundError', 'NameError', 'None', 'NotADirectoryError', 'NotImplemented', '
NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'PermissionError', 'ProcessLookupError'
, 'RecursionError', 'ReferenceError', 'ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopAsyncIteration', 'Stop
Iteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeErro
r', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'Unicode
Warning', 'UserWarning', 'ValueError', 'Warning', 'WindowsError', 'ZeroDivisionError', '__build_class__', '__debug__',
 '__doc__', '__import__', '__loader__', '__name__', '__package__', '__spec__', 'abs', 'all', 'any', 'ascii', 'bin', 'b
ool', 'breakpoint', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credit
s', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset',
 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'le
n', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'pr
int', 'property', 'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', '
str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip'