Python bit record 12: Exception handling

The exception handling mechanism is introduced so that the running program does not crash when an error occurs.

Common formats:

Try:command 1except:command 2

When command 1 performs an error, command 2 is executed. Command 2 is usually a self-defined error message or a system default prompt.

eg

#!/usr/bin/pythonwhile 1:        c = raw_input ("Input   ' C '  continue,otherwise logout: ")         if c  ==  ' C ':                 a = raw_input ("Input first number:")                  b = raw_input ("Input second number:")                 try:                          print float (a)/float (b)                          print  "+ + ++++++++++++++++++ "  &nbSp;             except zerodivisionerror :                         print  "The second number can ' t be zero!"                          print  "++++++++++++++++++++"                  except ValueError:                          print  "Please input number."                          print  "++++++++++++++++++++"         else:                 break

The first except or the second except statement is executed when the second entered by the user is 0 or is not a number.

Other formats:

Try:command 1except:command 2else:command 3

When command 1 is executed successfully, command 3 is executed and command 2 is not executed. If command 1 executes an exception, then command 2 is executed, and command 3 is not executed.

Try:command 1except:command 2else:command 3finally:command 4

In this format, finally (Command 4) is always executed regardless of which statement is executed.

Python bit record 12: Exception handling