Introduction to Python exception handling system (1)

Python built-in exception Architecture

The class hierarchy for built-in exceptions is:

BaseException
+-- SystemExit
+-- KeyboardInterrupt
+-- GeneratorExit
+-- 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
+-- Warning
+-- DeprecationWarning
+-- PendingDeprecationWarning
+-- RuntimeWarning
+-- SyntaxWarning
+-- UserWarning
+-- FutureWarning
+-- ImportWarning
+-- UnicodeWarning
+-- BytesWarning

Capture exceptions

Method 1: capture all exceptions

''' The first way to capture exceptions, capture all exceptions ''' try: a = B = c except t Exception, data: print Exception ,":", data ''' output: <type 'exceptions. exception '>: local variable' B' Referenced before assignment''

Method 2: Use the traceback module to view exceptions. Import the traceback module.

'''Second way to capture exceptions, use traceback to view exceptions ''' Try: A = B B = c Except t: Print traceback. print_exc () '''Output: Traceback (most recent call last ): File "test. py", line 20, in main A = B UnboundLocalError: local variable 'B' referenced before assignmen

Method 3: Use the sys module to trace the final exception

'''Third way to capture exceptions, use the sys module to capture exceptions ''' Try: A = B B = c Except t: Info = sys. exc_info () Print info Print info [0] Print info [1] ''' Output: (<Type 'exceptions. unboundlocalerror'>, UnboundLocalError ("local Variable 'B' referenced before assignment ",), <Traceback object at 0x00D243F0>) <Type 'exceptions. unboundlocalerror'> Local variable 'B' referenced before assignment '''