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For 2023 (and 2024 ...) - 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 Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own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))
Elements of an exception in Python - try, except, else, finally

All the elements of an exception handler in one example ... [here]

try - enters at the top and continues through the block
except - jump to there is an exception is thrown
else - run after the try block completes without exception thrown
finally - always run after the other blocks have completed

A correctly running block
try - else - finally
(and code loops completes)

  -bash-4.1$ python duff
  (bfor) Exception demonstration
  
  (try-) Please enter a Python value: 44
  (else) Input accepted
  (finl) Tidying up
  
  (done) Value received: 44
  -bash-4.1$


A block with an error
try - except - finally
(and code loops back to have another go)

  -bash-4.1$ python duff
  (bfor) Exception demonstration
  
  (try-) Please enter a Python value: forty
  (exce) Not acceptable!
  (exce) Message: name 'forty' is not defined
  (exce) Failure Type: NameError
  (finl) Tidying up
  
  (try-) Please enter a Python value:


Code

  while True:
    try:
      n = input("(try-) Please enter a Python value: ")
    except KeyboardInterrupt:
      print "(ex/k) You give up?"
      print "(ex/k) Won't break me that way"
    except Exception,e:
      print "(exce) Not acceptable!"
      print "(exce) Message: ",e
      print "(exce) Failure Type:",e.__class__.__name__
    else:
      print "(else) Input accepted"
      break
    finally:
      print "(finl) Tidying up\n"

(written 2015-02-28)

 
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)
  [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)


Back to
Seventh stay away this year - and it's still only February!
Previous and next
or
Horse's mouth home
Forward to
Graphing presentations in Python - huge data, numpy and matplotlib
Some other Articles
What is the difference between a function and a method?
Overnight accommodation in Melksham - if Well House Manor is full!
Combining tests into suites, and suites into bigger suites - Python and unittest
Graphing presentations in Python - huge data, numpy and matplotlib
Elements of an exception in Python - try, except, else, finally
Seventh stay away this year - and it's still only February!
Mutable v Immuatble objects in Python, and the implication
Reading command line parameters in Python
A first graph with Matplotlib in Python
Json is the new marshall, pickle and cPickle / Python
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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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