How to read lines only at the end of file?

[Alex Martelli]

Batista, Facundo wrote:

> Christopher Koppler wrote:
> 
> #- You could do the following:
> #-
> #- >>> f = file('filename.txt', 'r')
> #- >>> numberoflines = 10
> #- >>> for line in f.readlines()[-numberoflines:]:
> #- ...     print line
> #-
> #- which prints the last 10 lines of the file.
> 
> But if the file has 2GB? This method doesn't reads *all* the file?

Yes: f.readlines() does read all of the file.

You can use f.seek to position yourself at some distance
from the _end_ (in bytes, though) and .readlines() from there --
but if the last N lines are abnormally long you're still not
guaranteed to be able to give the last N lines without reading
all of the file, worst case.


Alex