--- "Michael P. Reilly" <[EMAIL PROTECTED]> wrote:
> On 9/24/05, Shitiz Bansal <[EMAIL PROTECTED]> wrote: > > > > Hi, > > > > How do i proceed if i am not sure about the number > of characters in the > > fist two lines and want to write in the third > line.is <http://line.is>there a way to skip two > lines and write on the third?? > > > > Also could anyone explain why the readline() did > not work. according to > > what i understand it should. > > *bob <[EMAIL PROTECTED]>* wrote: > > > > At 01:11 AM 9/24/2005, Shitiz Bansal wrote: > > >Hi, > > >I want to update a textfile using the r+ file > mode. > > >contents of file: > > > > > >abcd > > >efgh > > >ijkl > > >mnop > > >qrst > > >uvwx > > >yx12 > > > > > >my scripts is: > > > > > >file1=open("aa.txt",'r+') > > > > >>Instead of readline, use skip to position the > file to where you want to > > >>overwrite it. > > >>file1.seek(10) > > > > > > >file1.readline() > > >file1.readline() > > >file1.write("1234\n") > > >file1.close() > > > > > >This should replace the third line with 1234. > > >However it does nothing. > > > > > >Moreover the script: > > > > > >file1=open("aa.txt",'r+') > > >file1.write("1234\n") > > >file1.close() > > > > > >does replace the first line with 1234. > > > > > >could anyone explain what is happening? > > > > > >shitiz > > > > Hello Shitiz, > > I'm not sure if it is true anymore, I haven't gotten > to test it. But in the > olden days of C and standard libraries and UNIX, you > would open a file for > reading and writing and before you could switch > between read() and write() > you would have to perform a seek(). Usually > something like: > file.readline() # read line 1 > file.readline() # read line 2 > file.seek(0, 1) # move 0 bytes from current position > (no place) > file.write("1234\n") > file.close() > There may be one problem here. What you write will > overwrite line 3.... or > only part of line 3... or maybe all of line 3 and > some of line 4. It is good > to know how the file is structured before you write > to it, in case you end > up with unexpected data. If all your lines are four > characters plus a > newline, then you don't have to worry (most of us > aren't that lucky). > -Arcege > -- > There's so many different worlds, > So many different suns. > And we have just one world, > But we live in different ones. > __________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.com _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
