Search and write to .txt file
Piet van Oostrum
piet at cs.uu.nl
Tue Aug 11 15:30:12 CEST 2009
>>>>> Helvin <helvinlui at gmail.com> (H) wrote:
>H> Hi everyone,
>H> I am writing some python script that should find a line which contains
>H> '1' in the data.txt file, then be able to move a certain number of
>H> lines down, before replacing a line. At the moment, I am able to find
>H> the line '1', but when I use f.seek to move, and then rewrite, what I
>H> write goes to the end of the .txt file, instead of being adjusted by
>H> my f.seek.
>H> Do you know what way I should take?
>H> Data.txt is a file of 3 lines:
>H> with open('data.txt', 'r+') as f:
>H> firstread = f.readlines() # Take a snapshot of initial file
>H> f.seek(0,0) # Go back to beginning and search
>H> for line in f:
>H> print line
>H> if line.find('1'):
>H> print 'line matched'
>H> f.seek(1,1) # Move one space along
>H> f.write('house\n') # f.write overwrites the exact
>H> number of bytes.
>H> break # leave loop once '1' is found
Mixing an iterator on the file with direct calls (seek/write) isn't
going to work. The iterator does read ahead which causes the file
position not to be what you think it is.
>>> with open('data.txt', 'r+') as f:
... for line in f:
... print line, f.tell()
Piet van Oostrum <piet at cs.uu.nl>
URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4]
Private email: piet at vanoostrum.org
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