Insert character at a fixed position of lines

[Fredrik Lundh]

Francesco Pietra wrote:

> How to insert letter "A" on each line (of a very long list of lines)
> at position 22, i.e., one space after "LEU", leaving all other
> characters at the same position as in the original example:
> 
> 
> ATOM      1  N   LEU     1     146.615  40.494 103.776  1.00 73.04       1SG   2
> 
> In all lines"ATOM" is constant as to both position and string, while
> "LEU" is constant as to position only, i.e., "LEU" may be replaced by
> three different uppercase letters. Therefore, the most direct
> indication would be position 22.

you may find the fileinput module helpful, combined with the tips you've 
already gotten in this thread.

reference:

     http://docs.python.org/lib/module-fileinput.html

examples:

     http://effbot.org/librarybook/fileinput.htm
     http://blog.doughellmann.com/2007/03/pymotw-fileinput.html

</F>