For 2023 - we are now fully retired from IT training. We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.
Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!
I am also active in many other area and still look after a lot of web sites - you can find an index ((here)) |
Exceptions in Python
Rather than having to check ahead of time for every possible error, Python provides an exception handling capability too. Simply try to perform you action, and define what's to be done in an except block if the action you want can't be completed.
Here's an example in which we (try to) read an integer value from the user. If our user types a value that's not an integer, the exception is caught and the prompt repeated
def gnum(prompt):
while 1:
try:
rv = int(input(prompt+": "))
break
except:
print "eh?"
return rv
first = gnum("First number")
second = gnum("Second number")
print "Sum is "+str(first+second)
By the way - note the use of a named block of code (a function) to avoid the need to repeat code. Good programming practise! (written 2005-07-17, updated 2006-06-05)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles Y109 - Python - Exceptions [1042] Nested exceptions in Python - (2007-01-18) [1236] Trying things in Python - (2007-06-18) [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)
Some other Articles
Feast or famineManaging conflict and disappointmentOverloading of operators on standard objects in PythonCentral London Courses - Perl, PHP, Python, Tcl, MySQLExceptions in PythonBridging to the customer requirementGetting the lighting rightA word of admiration for the London cabbieA Strengthened CityWhat brings people to my web site?
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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.
Link to Ezine home page (for reading).
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