[2,3,4,7] --> "2-4,7" ?

[CezaryB]

On 5/29/2003 9:11 PM, George Young wrote:
> [python 2.3a1]
> I have a list of "names" like:
>   ['6','7','mx8','mx09','mx10','8','9','10','foo']
> which needs for concise and clear display to become a string like:
> 
>   "6-7,mx8-10,8-10,foo"
> 
> I.e., a name is an integer or an alphabetic prefix possibly followed
> by an integer.  The display must compress each set of succesive names
> having the same (possibly null) prefix and sequential integers.  The
> original order of names must be preserved.
> 
> I (hesitantly) post the following code that works, but makes me cringe
> anytime I see it, for it's clumsy unreadableness.  Can someone with
> a fresh mind see a clear and concise way to make my clear and concise
> name display?
> 

from __future__ import nested_scopes
import re

def collapse( input_sequence ):
     search = re.compile( '\d+$' ).search
     range_prefix = None
     range_start = 0
     range_last = 0
     item_last = None
     result_list = []

     def append_last( ):
         if range_prefix is not None:
             if range_start == range_last:
                 result_list.append( item_last )
             else:
                 result_list.append( range_prefix + str( range_start ) + '-' + str( 
range_last ) )

     for item in input_sequence:
         found = search( item )
         if found is None:
             append_last( )
             result_list.append( item )
             range_prefix = None
             continue
         start = found.start( )
         prefix = item[:start]
         value = int( item[start:] )
         if prefix == range_prefix and value == range_last + 1:
             range_last = value
         else:
             append_last( )
             range_prefix = prefix
             range_start = value
             range_last = value
         item_last = item

     append_last( )
     return ','.join( result_list )

---
CB