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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Trying things in Python

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)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
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)


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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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