how to delete or change...

[John Hunter]

>>>>> "Shagshag13" == Shagshag13  <shagshag13 at yahoo.fr> writes:

    >> There are some unknown's here that would be helpful to know.
    >> You say it's a text file but then talk about opening in binary.
    >> Is it ASCII?

    Shagshag13> yes, it's an ascii file (i try to open it in binary to
    Shagshag13> do bytes operations instead of lines operations)

    >> How large all the files? Is it feasible for you to work in
    >> memory?

    Shagshag13> No, i can't (huge file between 1,5 and 2,5 go)

    >> Also, you say when you tried the binary seek you got an I/O
    >> error.  Was there anything informative about that error that
    >> you can post?

    >>>> f2 = file('d:/test.txt', 'rwb') f2.seek(-5, 2) f2.read(5)
    Shagshag13> 'TUR\n'
    >>>> f2.seek(-5, 2) f2.write('new')
    Shagshag13> Traceback (most recent call last): File
    Shagshag13> "<pyshell#99>", line 1, in ?  f2.write('new') IOError:
    Shagshag13> (0, 'Error')

    Shagshag13> Maybe i miss something ?

Yes, this can be confusing

`open(filename[, mode[, bufsize]])'
     Return a new file object (described earlier under Built-in Types).
     The first two arguments are the same as for `stdio''s `fopen()':
     FILENAME is the file name to be opened, MODE indicates how the
     file is to be opened: `'r'' for reading, `'w'' for writing
     (truncating an existing file), and `'a'' opens it for appending
     (which on _some_ UNIX systems means that _all_ writes append to
     the end of the file, regardless of the current seek position).

     Modes `'r+'', `'w+'' and `'a+'' open the file for updating (note
     that `'w+'' truncates the file).  Append `'b'' to the mode to open
     the file in binary mode, on systems that differentiate between
     binary and text files (else it is ignored).  If the file cannot be
     opened, `IOError' is raised.

Note that 'w' truncates the file (which you clearly don't want) and
'a' appends to the end regardless of seek position.  What you want is
'r+b'.  I think the doc string could be a little clearer here ....

fname = 'somefile.dat'
f2 = open(fname, 'r+b')
f2.seek(-5,2)
f2.write('John')

Hope this helps,
John Hunter