Python's exception handling mechanism

Use try...except to catch exceptions

try:
	# Business implementation code
	...
except (Error1, Error2, ...) as e:
	# Handling code after exception
	...

Inheritance relationship of exception class

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

Access exception information

try:
	statement
except Exception as e:
	# Error number and details of access exception
	print(e.args)
	# Error number of access exception
	print(e.errno)
	# Access exception details
	print(e.strerror)

Block else

s = input('Please enter divisor:')
try:
	result = 20 / int(s)
	print("20 Divide%s The result is:%g" % (s, result))
except ValueError:
	print("Wrong value, you must enter a number")
except ArithmeticError:
	print("Arithmetic error, cannot enter 0")
else:
	print("No exception occurred")

Block finally

try:
	statement
except Exception as e:
	# Exception handling block
	...
else:
	# When no exception occurs
	...
finally:
	# No matter whether there is an exception or not, it will execute
	...

Custom exception handling

Use raise to throw an exception

• When an error occurs in the program, the system will automatically throw an exception. In addition, Python allows programs to use the raise statement to throw their own exceptions

Custom exception class

1. Custom exception class

class MyException(Exception):
	pass

1. Use custom exception class

raise MyException("Custom exception information")