Search and write to .txt file

[Mark Lawrence]

Helvin wrote:
> Hi everyone,
> 
> I am writing some python script that should find a line which contains
> '1' in the data.txt file, then be able to move a certain number of
> lines down, before replacing a line. At the moment, I am able to find
> the line '1', but when I use f.seek to move, and then rewrite, what I
> write goes to the end of the .txt file, instead of being adjusted by
> my f.seek.
> 
> Do you know what way I should take?
> 
> Data.txt is a file of 3 lines:
>    line1
>    line2
>    line3
> 
> Code:
> 
>    with open('data.txt', 'r+') as f:
>        firstread = f.readlines()   # Take a snapshot of initial file
> 
>        f.seek(0,0)    # Go back to beginning and search
>        for line in f:
>            print line
>            if line.find('1'):
>                print 'line matched'
>                f.seek(1,1)       # Move one space along
>                f.write('house\n')     # f.write overwrites the exact
> number of bytes.
>                break                    # leave loop once '1' is found
> 
>        f.seek(0,0)              # Go back to beginning, and read
> data.txt again
>        lastread = f.readlines()
> 
>        print 'firstread is', firstread
>        print 'lastread is', lastread
> 
> This shouldn't be too difficult, but I don't know how. > <
> Help appreciated!
You can't mix and match the file iterator "for line in f" with the seek 
method.  You already have the data in firstread, why not process it from 
there, i.e. "for line in firstread".  Also look at the docs for the find 
method, it doesn't return what you think it does.

-- 
Kindest regards.

Mark Lawrence.