reading specific lines of a file

[Nick Vatamaniuc]

Yi,
Use the linecache module. The documentation states that :
"""
The linecache module allows one to get any line from any file, while
attempting to optimize internally, using a cache, the common case where
many lines are read from a single file.
>>> import linecache
>>> linecache.getline('/etc/passwd', 4)
'sys:x:3:3:sys:/dev:/bin/sh\012'
"""

Please note that you cannot really skip over the lines unless each has
a fixed known size. (and if all lines have a fixed, known size then
they can be considered as 'records' and you can use seek() and other
random access magic. That is why sometimes it is a lot faster to use
fixed length rows in a database => increase the speed of search but at
the expense of wasted space! - but this is a another topic for another
discussion...).

So the point is that you won't be able to jump to line 15000 without
reading lines 0-14999. You can either iterate over the rows by yourself
or simply use the 'linecache' module like shown above. If I were you I
would use the linecache, but of course you don't mention anything about
the context of your project so it is hard to say.

Hope this helps,
Nick Vatamaniuc


Yi Xing wrote:
> Hi All,
>
> I want to read specific lines of a huge txt file (I know the line #).
> Each line might have different sizes. Is there a convenient and fast
> way of doing this in Python? Thanks.
> 
> Yi Xing