Are you used to writing long sections of code to validate user input? Perhaps you are, or perhaps you have shortened such code over the years using Regular Expressions where you can specify a pattern to be matched. One regular expression can replace 30 lines of other code.

But in Python, Java and some other languages there's an even more elegant alternative in some circumstances - exceptions. The idea is that you try to perform the action you require on your input data rather than 100% validating it first. If the action works, great and if it fails you catch the exception and handle the error condition in that block.

Like an example? Here's a piece of Python code to read an integer from the program's user, and to keep re-prompting if the user enters a value that cannot be treated as a legitimate integer.

while 1:
  val = raw_input("give an integer ... ")
  try:
    ival = int(val)
    break
  except:
    print "an integer is a WHOLE NUMBER! "
print ival
(written 2007-06-18)

 Y109 - Python - Exceptions
  [381] Exceptions in Python - (2005-07-17)
  [1042] Nested exceptions in Python - (2007-01-18)
  [2018] UnboundLocalError - Python Message - (2009-01-31)
  [2281] Python - using exceptions to set a fallback - (2009-07-12)
  [2368] Python - fresh examples of all the fundamentals - (2009-08-20)
  [2408] Robust user input (exception handling) example in Python - (2009-09-17)
  [2622] Handling unusual and error conditions - exceptions - (2010-02-03)
  [2994] Python - some common questions answered in code examples - (2010-10-10)
  [2998] Using an exception to initialise a static variable in a Python function / method - (2010-10-13)
  [3177] Insurance against any errors - Volcanoes and Python - (2011-02-19)
  [3433] Exceptions - a fail-safe way of trapping things that may go wrong - (2011-09-11)
  [3441] Pressing ^C in a Python program. Also Progress Bar. - (2011-09-15)
  [3664] Error checking in a Python program - making your program robust via exceptions - (2012-03-22)
  [3913] How many times ... has this loco headed west through Tenby? - Python exceptions - (2012-11-05)
  [3930] Reporting the full stack trace when you catch a Python exception - (2012-11-22)
  [4029] Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (2013-03-04)
  [4161] Python varables - checking existance, and call by name or by value? - (2013-08-27)
  [4444] Elements of an exception in Python - try, except, else, finally - (2015-02-28)

Back to Outputting numbers as words - MySQL with Perl or PHP

Previous and next or Horse's mouth home

Forward to What proportion of our web traffic is robots?

Fancy going to Glastonbury?
End of File on a Java BufferedReader
The kind spirit of Melksham
What proportion of our web traffic is robots?
Trying things in Python
Outputting numbers as words - MySQL with Perl or PHP
A review of a week and a trip to Brugge
Horses of Brugge
Bathtub example
Sur le Continent