Little direction please Python MySQL

[Tim Chase]

>> Files are fixed format no field delimiters, fields are position and
>> length records are terminated by newline.
> 
> Assuming no COMPUTATIONAL fields, it should be easy enough to split each line up into fixed-length pieces, e.g. assuming a simple example
> 
>     01 Sample-Record.
>       02 Field-1 pic XXX.
>       02 Field-2 pic XXXX.
>       02 Field-3 pic XXXXX.
> 
> then a Python sequence that read one line's worth of fields might be
> 
>     line = infile.read()
>     (field_1, field_2, field_3) = (line[0:3], line[3:7], line[7:12])


A recent posting on the list offered an elegant solution to this 
with a function something like

   def splitter(s, *lens):
     offset = 0
     pieces = []
     for length in lens:
       pieces.append(s[offset:offset+length])
       offset += length
     return pieces


which could then be used to simplify that to

   (f1, f1, f3) = splitter(line, 3, 4, 5)

It may not be quite so significant with just 3 items, but the OP 
mentioned having a large number of items in each record.  One 
could even use something like a mapping for this.  Something like:

   field_lens = [
     ("field1", 3),
     ("field2", 4),
     ("field3", 5),
     # stacks more
     ]
   fields = dict(zip(
     (name for name, _ in field_lens),
     splitter(line, *[length for _, length in field_lens])
     ))
   something = "Whatever %s you want" % fields["field2"]

If you like this method, you can even make a more targeted 
splitter() function and add some function mappings like

   field_lens = [ # somewhat similar to your Cobol masks
     ("field1", 3, str),
     ("field2", 4, int),
     ("field3", 5, float),
     ("field4", 17, lambda s: s.strip().upper() ),
     # stacks more
     ]


   def splitter(s, field_lens):
     pieces = {}
     offset = 0
     for name, length, fn in field_lens:
       pieces[name] = fn(s[offset:offset+length])
       offset += length
     return pieces

   bits = splitter(line), field_lens)
   # do addition of int+float rather than string concat
   print bits["field2"] + bits["field3"]

-tkc