> You can also keep track of the absolute position of the lines in the file, > etc, or step back looking for newlines, etc, but it's not handy.
How would I keep track of the absolute position of the lines? I have tried to use the files.seek() command with the files.tell() command and it does not seem to work. The files.tell() command seems to give me a number but when I use the files.next() command with xreadlines it does not change the line number the next time I use files.tell(). Thanks, Brett --- On Thu, 2/26/09, bearophileh...@lycos.com <bearophileh...@lycos.com> wrote: > From: bearophileh...@lycos.com <bearophileh...@lycos.com> > Subject: Re: Using xreadlines > To: python-list@python.org > Date: Thursday, February 26, 2009, 8:09 PM > Brett Hedges: > > My question is how do I go to a previous line in the > file? xreadlines has a file.next() statement that gives the > next line, and I need a statement that gives me the previous > line.< > > In modern versions of Python you usually don't need > xreadlines, > because files are iterable. > > If your files are small, you can just read all the lines in > a list > with open(...).readlines(), and then just use the item of > the list > with the n-1 index. > > If the file is quite large or you like to keep things lazy, > then you > have to keep memory of the previous line, using an > auxiliary variable. > You can also wrap this idiom into a generator function (or > iterable > class, probably) that yields items and keeps memory of the > last one > (but you can't ask the previous of the first item, of > course). > > You can also keep track of the absolute position of the > lines in the > file, etc, or step back looking for newlines, etc, but > it's not handy. > > Bye, > bearophile > -- > http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
