tail

[Avi Gross]

Marco,
I think it was made clear from the start that "text" files in the classic sense have no random access method at any higher level than reading a byte at some offset from the beginning of the file, or back from the end when it has not grown.
The obvious fact is that most of the time the lines are not of fixed widths and you have heard about multiple byte encodings and how the ends of lines can vary.

When files get long enough that just reading them from the start as a whole, or even in chunks, gets too expensive, some people might consider some other method. Log files can go on for years so it is not uncommon to start a new one periodically and have a folder with many of them in some order. To get the last few lines simply means finding the last file and reading it, or if it is too short, getting the penultimate one too.
And obviously a database or other structure might work better which might make each "line" a record and index them.
But there are ways to create your own data that get around this such as using an encoding with a large but fixed width for every character albeit you need more storage space. But if the goal is a general purpose tool, internationalization from ASCII has created a challenge for lots of such tools.


-----Original Message-----
From: Marco Sulla <Marco.Sulla.Python at gmail.com>
To: Dennis Lee Bieber <wlfraed at ix.netcom.com>
Cc: python-list at python.org
Sent: Sat, May 7, 2022 9:21 am
Subject: Re: tail

On Sat, 7 May 2022 at 01:03, Dennis Lee Bieber <wlfraed at ix.netcom.com> wrote:
>
>        Windows also uses <cr><lf> for the EOL marker, but Python's I/O system
> condenses that to just <lf> internally (for TEXT mode) -- so using the
> length of a string so read to compute a file position may be off-by-one for
> each EOL in the string.

So there's no way to reliably read lines in reverse in text mode using
seek and read, but the only option is readlines?
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