title: Writing/parsing text file with fixed width lines
body: <p>I'm a newbie to Python and I'm looking at using it to write some hairy EDI stuff that our supplier requires.</p>
  
  <p>Basically they need an 80-character fixed width text file, with certain "chunks" of the field with data and others left blank.  I have the documentation so I know what the length of each "chunk" is.  The response that I get back is easier to parse since it will already have data and I can use Python's "slices" to extract what I need, but I can't assign to a slice - I tried that already because it sounded like a good solution, and it didn't work since Python strings are immutable :)</p>
  
  <p>Like I said I'm really a newbie to Python but I'm excited about learning it :) How would I go about doing this?  Ideally I'd want to be able to say that range 10-20 is equal to "Foo" and have it be the string "Foo" with 7 additional whitespace characters (assuming said field has a length of 10) and have that be a part of the larger 80-character field, but I'm not sure how to do what I'm thinking. </p>