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Keeping your regular expressions simple

There's something macho about programmers when it comes to regular expressions - so often they'll try and do the whole job in a single regular expression when doing a two stage process is much more logical, much quicker in operation, and far easier to code.

Take a requirement that came up this morning, for example, to extract data from a netlist. The data to be handled might look like:
[5560] = !V5*V6*V7*!V8 + [5223]
and the requirement is to return a list elements separated by = or + signs, and then to return a list of nodes or inputs within those elements. In other words, what's wanted is:
['5560']
['!V5', 'V6', 'V7', '!V8']
['5223']


I think I have rather made my point already by how I described the requirement, haven't I? Two regular expressions ...

I'm running a Python course, so the example's in Python ... full source code and more Python regular expression examples available!
(written 2006-04-05, updated 2006-06-05)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Q806 - Regular Expression Cookbook
  [3788] Getting more than a yes / no answer from a regular expression pattern match - (2012-06-30)
  [3218] Matching a license plate or product code - Regular Expressions - (2011-03-28)
  [2804] Regular Expression Myths - (2010-06-13)
  [2727] Making a Lua program run more than 10 times faster - (2010-04-16)
  [2702] First and last match with Regular Expressions - (2010-04-02)
  [2608] Search and replace in Ruby - Ruby Regular Expressions - (2010-01-31)
  [2563] Efficient debugging of regular expressions - (2010-01-04)
  [2165] Making Regular Expressions easy to read and maintain - (2009-05-10)
  [1840] Validating Credit Card Numbers - (2008-10-14)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1230] Commenting a Perl Regular Expression - (2007-06-12)

Y115 - Additional Python Facilities
  [4709] Some gems from Intermediate Python - (2016-10-30)
  [4593] Command line parameter handling in Python via the argparse module - (2015-12-08)
  [4536] Json load from URL, recursive display, Python 3.4 - (2015-10-14)
  [4451] Running an operating system command from your Python program - the new way with the subprocess module - (2015-03-06)
  [4439] Json is the new marshall, pickle and cPickle / Python - (2015-02-22)
  [4298] Python - an interesting application - (2014-09-18)
  [4211] Handling JSON in Python (and a csv, marshall and pickle comparison) - (2013-11-16)
  [4085] JSON from Python - first principles, easy example - (2013-05-13)
  [3469] Teaching dilemma - old tricks and techniques, or recent enhancements? - (2011-10-08)
  [3442] A demonstration of how many Python facilities work together - (2011-09-16)
  [3089] Python regular expressions - repeating, splitting, lookahead and lookbehind - (2010-12-17)
  [2790] Joining a MySQL table from within a Python program - (2010-06-02)
  [2786] Factory methods and SqLite in use in a Python teaching example - (2010-05-29)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [2764] Python decorators - your own, staticmethod and classmethod - (2010-05-14)
  [2746] Model - View - Controller demo, Sqlite - Python 3 - Qt4 - (2010-04-29)
  [2745] Connecting Python to sqlite and MySQL databases - (2010-04-28)
  [2721] Regular Expressions in Python - (2010-04-14)
  [2655] Python - what is going on around me? - (2010-02-28)
  [2462] Python - how it saves on compile time - (2009-10-20)
  [2435] Serialization - storing and reloading objects - (2009-10-04)
  [2407] Testing code in Python - doctest, unittest and others - (2009-09-16)
  [1876] Python Regular Expressions - (2008-11-08)
  [1337] A series of tyre damages - (2007-09-08)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1149] Turning objects into something you can store - Pickling (Python) - (2007-04-15)
  [1136] Buffering output - why it is done and issues raised in Tcl, Perl, Python and PHP - (2007-04-06)
  [1043] Sending an email from Python - (2007-01-18)
  [901] Python - listing out the contents of all variables - (2006-10-21)
  [753] Python 3000 - the next generation - (2006-06-09)
  [663] Python to MySQL - (2006-03-31)
  [463] Splitting the difference - (2005-10-13)
  [239] What and why for the epoch - (2005-03-08)
  [208] Examples - Gadfly, NI Number, and Tcl to C interface - (2005-02-10)
  [183] The elegance of Python - (2005-01-19)


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