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.
Python - using exceptions to set a fallback
In Python, you should use exceptions to catch error conditions such as files that you're unable to open, broken network connections, and user inputs which give a problem - it's all very well putting traditional checks in your code, but you'll be well advised to use try
as well for additional security.
You can also use exceptions as a safety net to set the fallback value for a variable if it hasn't otherwise been defined, as in this example:
# Lots of code that SHOULD set "status" variable ...
status = "OK"
print "Code carries on, status is ",status
With multiple except
clauses, Python can handle different errors in different ways - if you're going to use this facility, list the most specific exceptions first, as Python will use whichever one matches first.
Note that in Python, you can also raise
your own exceptions too - and you are strongly advised to do so when you want to return an 'error' from a function rather than a value
. For example, you should raise an exception in a function that returns the number of children someone has, but the function cannot determine a result - it should NOT return a cardinal or special value such as 99 or -1 as that would make the calling code and handling of the results more complex (and, one day, someone MIGHT be a sperm donor and have fathered 99 children!) (written 2009-07-12)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articlesY109 - Python - Exceptions 
Exceptions in Python - (2005-07-17) 
Nested exceptions in Python - (2007-01-18) 
Trying things in Python - (2007-06-18) 
UnboundLocalError - Python Message - (2009-01-31) 
Python - fresh examples of all the fundamentals - (2009-08-20) 
Robust user input (exception handling) example in Python - (2009-09-17) 
Handling unusual and error conditions - exceptions - (2010-02-03) 
Python - some common questions answered in code examples - (2010-10-10) 
Using an exception to initialise a static variable in a Python function / method - (2010-10-13) 
Insurance against any errors - Volcanoes and Python - (2011-02-19) 
Exceptions - a fail-safe way of trapping things that may go wrong - (2011-09-11) 
Pressing ^C in a Python program. Also Progress Bar. - (2011-09-15) 
Error checking in a Python program - making your program robust via exceptions - (2012-03-22) 
How many times ... has this loco headed west through Tenby? - Python exceptions - (2012-11-05) 
Reporting the full stack trace when you catch a Python exception - (2012-11-22) 
Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (2013-03-04) 
Python varables - checking existance, and call by name or by value? - (2013-08-27) 
Elements of an exception in Python - try, except, else, finally - (2015-02-28)
Some other Articles
Great new diagrams for our notes ... Python releasesStrings as collections in PythonEveryone is in the customer relations businessChecking robots.txt from PythonPython - using exceptions to set a fallbackCreating and iterating through Python listsUnderstanding the new local government structure in WiltshireFirst courses for 2010Python classes / courses - what version do we train on?Who is Marc Schneider of Multilingual Search Engine Optimization Inc
4759 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 at 50 posts per page
This is a page archived from The Horse's Mouth at
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.
Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).