A bug with file.tell()?

Andrew Dalke adalke at mindspring.com
Fri Sep 10 09:11:27 CEST 2004


Nick Jacobson wrote:
> Is this a bug?

   [example of mixing iterator-style line reads from a
    file and tell]

No, it's a documented behaviour.

http://docs.python.org/lib/bltin-file-objects.html

] In order to make a for loop the most efficient way
] of looping over the lines of a file (a very common
] operation), the next() method uses a hidden read-ahead
] buffer. As a consequence of using a read-ahead
] buffer, combining next() with other file methods (like
] readline()) does not work right. However, using seek()
] to reposition the file to an absolute position will
] flush the read-ahead buffer.

> This code involves the file methods "seek" and "tell".  Even though
> the file pointer is in the middle of the file, "tell" returns a
> position at the end of the file!

That means the underlying file handle is at
the end and everything remaining is in memory.



				Andrew
				dalke at dalkescientific.com



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