reposition a column

[Vlastimil Brom]

2009/11/25 Francesco Pietra <francesco.pietra at accademialucchese.it>:
> Hi:
>
> In a pdb file made of lines "ATOM .." (see attachment as I was unable
> to obtain plain text with gmail) I would like to reposition the second
> "W" from column 19 to 17 ( (Python numbering; in pdb numbering it
> would be 20 18). I started with bold slices, then I was unable to
> complete the script. Much obliged for help.
>
> francesco pietra
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>
Hi,
using only string slices, you can probably do something like the
following (if I underestand the specification correctly, i.e. to swap
the two columns under the given condition).
An alternative is to swap the indices directly using list.
Also a regular expression replace with re.sub might be viable
(probably the shortest one)...

hth,
  vbr

######################################

scale = """          1         2         3         4         5         6
012345678901234567890123456789012345678901234567890123456789012345"""
data_line = "ATOM      1  W     W     1       0.690  35.960  33.300  1.00  0.00"

if data_line [19] == 'W':
    output_line = data_line [0:17]+data_line [19]+data_line
[18]+data_line [17]+data_line [20:]
# alternatively
    ch_19, ch_17 = data_line [19], data_line [17]
    data_lst = list(data_line)
    data_lst[17] = ch_19
    data_lst[19] = ch_17
    output_line_2 = "".join(data_lst)
    print output_line_2 == output_line

else:
    output_line = data_line

print scale
print data_line
print scale
print output_line
print "=" * 66