Reading by positions plain text files

[Tim Chase]

On 11/30/2010 08:03 PM, javivd wrote:
> On Nov 30, 11:43 pm, Tim Harig<user... at ilthio.net>  wrote:
>>> VARIABLE NAME      POSITION (COLUMN) IN FILE
>>> var_name_1                 123-123
>>> var_name_2                 124-125
>>> var_name_3                 126-126
>>> ..
>>> ..
>>> var_name_N                 512-513 (last positions)
>>
> and no, MRAB, it's not the similar problem (at least what i understood
> of it). I have to associate the position this file give me with the
> variable name this file give me for those positions.

MRAB may be referring to my reply in that thread where you can do 
something like

   OFFSETS = 'offsets.txt'
   offsets = {}
   f = file(OFFSETS)
   f.next() # throw away the headers
   for row in f:
     varname, rest = row.split()[:2]
     # sanity check
     if varname in offsets:
       print "[%s] in %s twice?!" % (varname, OFFSETS)
     if '-' not in rest: continue
     start, stop = map(int, rest.split('-'))
     offsets[varname] = slice(start, stop+1) # 0-based offsets
     #offsets[varname] = slice(start+1, stop+2) # 1-based offsets
   f.close()

   def do_something_with(data):
     # your real code goes here
     print data['var_name_2']

   for row in file('data.txt'):
     data = dict((name, row[offsets[name]]) for name in offsets)
     do_something_with(data)

There's additional robustness-checks I'd include if your 
offsets-file isn't controlled by you (people send me daft data).

-tkc