Changing the middle of strings in a list--I know there is a better way.

[Ben]

On Oct 21, 1:53 pm, "J. Cliff Dyer" <j... at sdf.lonestar.org> wrote:
> On Tue, 2008-10-21 at 10:28 -0700, Ben wrote:
> > Hello All:
>
> > I am new to Python, and I love it!! I am running 2.6 on Windows. I
> > have a flat text file here is an example of 3 lines with numbers
> > changed for security:
>
> > 999999999088869199999999990200810999999
> > 999999999088869199999999990200810999999
> > 999999999088869199999999990200810999999
>
> > I want to be able to replace specific slices with other values. My
> > code below reads a file into a list of strings. Since strings are
> > immutable I can't assign different values to a specific slice of the
> > string. How can I accomplish this? I read some posts on string
> > formatting but I am having trouble seeing how I can use those features
> > of the language to solve this problem.
>
> > The code below just puts an 'R' at the beginning of each line like
> > this:
>
> > R999999999088869199999999990200810999999
> > R999999999088869199999999990200810999999
> > R999999999088869199999999990200810999999
>
> > But what I want to do is change the middle of the string. Like this:
>
> > R999999999088869CHANGED99990200810999999
> > R999999999088869CHANGED99990200810999999
> > R999999999088869CHANGED99990200810999999
>
> Well, it depends on what you want.  Do you want to replace by location
> or by matched substring?  One of the following functions might help.
>
> lines = ['999999999088869199999999990200810999999'
>          '99999999088869199999999990200810999999'
>          '9999999088869199999999990200810999999']
>
> def replace_by_location(string, replacement, start, end):
>     return string[:start] + replacement + string[end:]
>
> def replace_by_match(string, substr, replacement):
>     return replacement.join(string.split(substr))
>
> location_lines = [replace_by_location(x, 'CHANGED', 15, 22) for x in lines]
> match_lines = [replace_by_match(x, '1999999', 'CHANGED') for x in lines]
>
> print location_lines
> print match_lines
>
> Cheers,
> Cliff
>
> > #My Current Code
>
> > # read the data file in as a list
> > F = open('C:\\path\\to\file', "r")
> > List = F.readlines()
> > F.close()
>
> > #Loop through the file and format each line
> > a=len(List)
> > while a > 0:
>
> >     List.insert(a,"2")
> >     a=a-1
>
> > # write the changed data (list) to a file
> > FileOut = open("C:\\path\\to\\file", "w")
> > FileOut.writelines(List)
> > FileOut.close()
>
> > Thanks for any help and thanks for helping us newbies,
>
> > -Ben
> > --
> >http://mail.python.org/mailman/listinfo/python-list
>
>

Thanks for your help, this explains it I needed a little mental jump
start.

-Ben