[Python-Dev] lifting of prohibition against readlines inside a "for line in file" in Py3?

[rdmurray at bitdance.com]

On Wed, 18 Feb 2009 at 21:25, Antoine Pitrou wrote:
> Nick Coghlan <ncoghlan <at> gmail.com> writes:
>>
>> I *think* the 2.x system had an internal buffer that was used by the
>> file iterator, but not by the file methods. With the new IO stack for
>> 3.0, there is now a common buffer shared by all the file operations
>> (including iteration).
>>
>> However, given that the lifting of the restriction is currently
>> undocumented, I wouldn't want to see a commitment to keeping it lifted
>> until we know that it won't cause any problems for the io-in-c rewrite
>> for 3.1 (hopefully someone with more direct involvement with that
>> rewrite will chime in, since they'll know a lot more about it than I do).
>
> As you said, there is no special buffering for the file iterator in 3.x, which
> means the restriction could be lifted (actually there is nothing relying on this
> restriction in the current code, except perhaps the "telling" flag in
> TextIOWrapper).

Currently I have python (2.x) code that uses 'readline' instead of 'for
x in myfile' in order to avoid the 'for' buffering (ie: be presented
with the next line as soon as it is written to the other end of a pipe,
instead of waiting for the buffer to fill).  Does "no special buffering"
mean that 'for' doesn't use a read-ahead buffer in p3k, or that readline
does use such a buffer, because the latter could make my code break
unexpectedly when porting to p3k.

--RDM