Error Handling and Exception

• exception classes:
• BaseException(base class),
  • Exception,
  • AttributeError, IndexError,
  • IOError, KeyboardInterrupt,
  • KeyError,
  • NameError
  • SyntaxError
  • TypeError
  • ValueError

• try:
      expressions
  except (ValueError, Index Error) as err: # can be any exception class, as err is optional (to catch the error)
      print(err)
  except Exception as err:
      print("general exception" # handle all exception types
  else:
      print("\n")
  finally:
      print("final clause")  # finally will always be executed
  
  # notice:
  # variable "err" will be deleted after the try block
  

• finally block will always be executed
• user can define error types

• class MyInputError(Exception):
      """Exception raised when there're errors in input"""
      def __init__(self, value): 
          self.value = value
      def __str__(self):
          return ("{} is invalid input".format(repr(self.value)))
  
  try:
      raise MyInputError(1) # Throw
  except MyInputError as err:
      print('error: {}'.format(err)
  

• throw error by raise()

• # err_reraise.py
  
  def foo(s):
      n = int(s)
      if n==0:
          raise ValueError('invalid value: %s' % s)
      return 10 / n
  
  def bar():
      try:
          foo('0')
      except ValueError as e:
          print('ValueError!')
          raise
  
  bar()
  

• assert
  • throw AssertionError
• logging use the logging module

pdb

pdb commands

• Single Step run

  • $ python -m pdb err.py
    

• Set Trace

  • import pdb
    
    pdb.set_trace() # will stop here
    

• debugger commands

Profiling

cProfile

profilers in python

python -m cProfile <file>

line_profiler

line_profiler

magic commands

Modules

Logging

logging to log error (or info) messages to files and check