[Python-Dev] xreadlines : readlines :: xrange : range

[Guido van Rossum]

> Think like an implementer here <0.5 wink>:  they've lost track of how many
> characters are in the buffer despite a locking scheme whose purpose is to
> prevent that.  If it were my implementation, that would be a top-priority
> bug no matter how silly the first program I saw that triggered it.

The locking prevents concurrent threads accessing the stream.

But mixing reads and writes (without intervening fseek etc.) is
illegal use of the stream, and the C standard allows them to be lax
here, even if the program was single-threaded.

In other words: the locking is so good that it serializes the sequence
of reads and writes; but if the sequence of reads and writes is
illegal, they don't guarantee anything.

--Guido van Rossum (home page: http://www.python.org/~guido/)