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Pressing ^C in a Python program. Also Progress Bar.

If you want to stop a user interrupt via ^C aborting your program, you can catch a KeyboardInterrupt in Python. There's an example [here] which I wrote earlier today. It also shows how important it might be to use two try/except blocks rather than one - I've specified two inputs in the same block and, very irritatingly (and to make a point!) an entry of ^C to the second question knocks you back to the first question again for re-answering.

Once you disable ^C, you need to find some way of killing your process should an emergency need arise. Running on Unix / Linux systems from a command line, you can use ^Z to suspend the process and the use kill %!. You could also report the process number (via getpid (sample call [here]) to a .pid file, or to the user ...

... and another way to allow ^C to work in some circumstances is to look for it being pressed twice within a very short time - "double click"ed. There's a further example showing that [here]. That example also shows a progress bar in Python. Note ...
• use of \r rather than \n to send the cursor back but remain on the same line
• use of flush to ensure that output isn't buffered
• use of formatted fixed width output to ensure that each new report fully replaced previous one and doesn't leave spurious characters hen a short line replaces a longer one.
(written 2011-09-15, updated 2011-09-16)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y109 - Python - Exceptions
  [4161] Python varables - checking existance, and call by name or by value? - (2013-08-27)
  [4029] Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (2013-03-04)
  [3930] Reporting the full stack trace when you catch a Python exception - (2012-11-22)
  [3913] How many times ... has this loco headed west through Tenby? - Python exceptions - (2012-11-05)
  [3664] Error checking in a Python program - making your program robust via exceptions - (2012-03-22)
  [3433] Exceptions - a fail-safe way of trapping things that may go wrong - (2011-09-11)
  [3177] Insurance against any errors - Volcanoes and Python - (2011-02-19)
  [2998] Using an exception to initialise a static variable in a Python function / method - (2010-10-13)
  [2994] Python - some common questions answered in code examples - (2010-10-10)
  [2622] Handling unusual and error conditions - exceptions - (2010-02-03)
  [2408] Robust user input (exception handling) example in Python - (2009-09-17)
  [2368] Python - fresh examples of all the fundamentals - (2009-08-20)
  [2281] Python - using exceptions to set a fallback - (2009-07-12)
  [2018] UnboundLocalError - Python Message - (2009-01-31)
  [1236] Trying things in Python - (2007-06-18)
  [1042] Nested exceptions in Python - (2007-01-18)
  [381] Exceptions in Python - (2005-07-17)

Y212 - Python - Code testing, patterns, profiles and optimisation.
  [4326] Learning to program - comments, documentation and test code - (2014-11-22)
  [4090] Test Driven Development in Python - Customer Comes First - (2013-05-16)
  [3658] Using Make for a distribution - (2012-03-17)
  [3478] Testing your Python classes with the unittest package - how to - (2011-10-14)
  [3464] Passing optional and named parameters to python methods - (2011-10-04)
  [3442] A demonstration of how many Python facilities work together - (2011-09-16)
  [2616] Defining a static method - Java, Python and Ruby - (2010-02-01)
  [2123] Using Python with OpenOffice - (2009-04-09)
  [1555] Advanced Python, Perl, PHP and Tcl training courses / classes - (2008-02-25)
  [1148] Python decorators - wrapping a method call in extra code - (2007-04-15)
  [1146] __new__ v __init__ - python constructor alternatives? - (2007-04-14)
  [1140] Python GTK - Widget, Packing, Event and Feedback example - (2007-04-09)
  [235] Preparation for a day's work - (2005-03-04)


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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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