Flexible Collating (feedback please)

Ron Adam rrr at ronadam.com
Wed Oct 18 22:52:43 CEST 2006

I made a number of changes ...  (the new version is listed below)

These changes also resulted in improving the speed by about 3 times when all 
flags are specified.

Collating now takes about 1/3 (or less) time.  Although it is still quite a bit 
slower than a bare list.sort(), that is to be expected as collate is locale 
aware and does additional transformations on the data which you would need to do 
anyways.  The tests where done with Unicode strings as well.

Changed the flag types from integer values to a list of named strings. The 
reason for this is it makes finding errors easier and you can examine the flags 
attribute and get a readable list of flags.

A better regular expression for separating numerals.  It now separates numerals 
in the middle of the string.

Changed flag COMMA_IN_NUMERALS to IGNORE_COMMAS, This was how it was implemented.


This lets you collate decimal separated numbers correctly such as version 
numbers and internet address's.  It also prevents numerals from being 
interpreted as floating point or decimal.

It might make more since to implement it as PERIOD_IS_SEPARATOR. Needed?

Other minor changes to doc strings and tests were made.

Any feedback is welcome.



     A general purpose configurable collate module.

     Collation can be modified with the following keywords:

         CAPS_FIRST              -> Aaa, aaa, Bbb, bbb
         HYPHEN_AS_SPACE         -> Don't ignore hyphens
         UNDERSCORE_AS_SPACE     -> Underscores as white space
         IGNORE_LEADING_WS       -> Disregard leading white space
         NUMERICAL               -> Digit sequences as numerals
         IGNORE_COMMAS           -> Allow commas in numerals
         PERIOD_AS_COMMAS        -> Periods can separate numerals.

     * See doctests for examples.

     Author: Ron Adam, ron at ronadam.com

__version__ = '0.02 (pre-alpha) 10/18/2006'

import re
import locale
import string

locale.setlocale(locale.LC_ALL, '')  # use current locale settings

#  The above line may change the string constants from the string
#  module.  This may have unintended effects if your program
#  assumes they are always the ascii defaults.


class Collate(object):
     """ A general purpose and configurable collator class.
     def __init__(self, flags=[]):
         self.flags = flags
         self.numrex = re.compile(r'([\d\.]*|\D*)', re.LOCALE)
         self.txtable = []
         if HYPHEN_AS_SPACE in flags:
             self.txtable.append(('-', ' '))
         if UNDERSCORE_AS_SPACE in flags:
             self.txtable.append(('_', ' '))
         if PERIOD_AS_COMMAS in flags:
             self.txtable.append(('.', ','))
         if IGNORE_COMMAS in flags:
             self.txtable.append((',', ''))
         self.flags = flags

     def transform(self, s):
         """ Transform a string for collating.
         if not self.flags:
             return locale.strxfrm(s)
         for a, b in self.txtable:
             s = s.replace(a, b)
         if IGNORE_LEADING_WS in self.flags:
             s = s.strip()
         if CAPS_FIRST in self.flags:
             s = s.swapcase()
         if NUMERICAL in self.flags:
             slist = self.numrex.split(s)
             for i, x in enumerate(slist):
                     slist[i] = float(x)
                     slist[i] = locale.strxfrm(x)
             return slist
         return locale.strxfrm(s)

     def __call__(self, a):
         """ This allows the Collate class work as a sort key.

                 USE: list.sort(key=Collate(flags))
         return self.transform(a)

def collate(slist, flags=[]):
     """ Collate list of strings in place.

def collated(slist, flags=[]):
     """ Return a collated list of strings.
     return sorted(slist, key=Collate(flags).transform)

def _test():

     Sort (and sorted) normally order all words beginning with caps
     before all words beginning with lower case.

         >>> t = ['tuesday', 'Tuesday', 'Monday', 'monday']
         >>> sorted(t)     # regular sort
         ['Monday', 'Tuesday', 'monday', 'tuesday']

     Locale collation puts words beginning with caps after words
     beginning with lower case of the same letter.

         >>> collated(t)
         ['monday', 'Monday', 'tuesday', 'Tuesday']

     The CAPS_FIRST option can be used to put all words beginning
     with caps before words beginning in lowercase of the same letter.

         >>> collated(t, [CAPS_FIRST])
         ['Monday', 'monday', 'Tuesday', 'tuesday']

     The HYPHEN_AS_SPACE option causes hyphens to be equal to space.

         >>> t = ['a-b', 'b-a', 'aa-b', 'bb-a']
         >>> collated(t)
         ['aa-b', 'a-b', 'b-a', 'bb-a']

         >>> collated(t, [HYPHEN_AS_SPACE])
         ['a-b', 'aa-b', 'b-a', 'bb-a']

     used together to improve ordering in some situations.

         >>> t = ['sum', '__str__', 'about', '  round']
         >>> collated(t)
         ['  round', '__str__', 'about', 'sum']

         >>> collated(t, [IGNORE_LEADING_WS])
         ['__str__', 'about', '  round', 'sum']

         >>> collated(t, [UNDERSCORE_AS_SPACE])
         ['  round', '__str__', 'about', 'sum']

         >>> collated(t, [IGNORE_LEADING_WS, UNDERSCORE_AS_SPACE])
         ['about', '  round', '__str__', 'sum']

     The NUMERICAL option orders sequences of digits as numerals.

         >>> t = ['a5', 'a40', '4abc', '20abc', 'a10.2', '13.5b', 'b2']
         >>> collated(t, [NUMERICAL])
         ['4abc', '13.5b', '20abc', 'a5', 'a10.2', 'a40', 'b2']

     The IGNORE_COMMAS option prevents commas from seperating numerals.

         >>> t = ['a5', 'a4,000', '500b', '100,000b']
         >>> collated(t, [NUMERICAL, IGNORE_COMMAS])
         ['500b', '100,000b', 'a5', 'a4,000']

     The PERIOD_AS_COMMAS option can be used to sort version numbers
     and other decimal seperated numbers correctly.

         >>> t = ['5.1.1', '5.10.12','5.2.2', '5.2.19' ]
         >>> collated(t, [NUMERICAL, PERIOD_AS_COMMAS])
         ['5.1.1', '5.2.2', '5.2.19', '5.10.12']

     Collate also can be done in place by using collate() instead of

         >>> t = ['Fred', 'Ron', 'Carol', 'Bob']
         >>> collate(t)
         >>> t
         ['Bob', 'Carol', 'Fred', 'Ron']

     import doctest

if __name__ == '__main__':

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