[issue12053] Add prefetch() for Buffered IO (experiment)

[John O'Connor]

New submission from John O'Connor <tehjcon at gmail.com>:

A prefetch() method for Buffered IO may greatly assist 3rd party buffering among other gains. If nothing else, it is worth experimenting with. 

Discussion on the topic is here: http://mail.python.org/pipermail/python-ideas/2010-September/008180.html

A summary of the method proposed (by Antoine Pitrou):

prefetch(self, buffer, skip, minread)

Skip `skip` bytes from the stream.  Then, try to read at
least `minread` bytes and write them into `buffer`. The file
pointer is advanced by at most `skip + minread`, or less if
the end of file was reached. The total number of bytes written
in `buffer` is returned, which can be more than `minread`
if additional bytes could be prefetched (but, of course,
cannot be more than `len(buffer)`).

Arguments:
- `buffer`: a writable buffer (e.g. bytearray)
- `skip`: number of bytes to skip (must be >= 0)
- `minread`: number of bytes to read (must be >= 0 and <= len(buffer))

----------
components: IO
messages: 135731
nosy: benjamin.peterson, haypo, jcon, pitrou, stutzbach
priority: normal
severity: normal
status: open
title: Add prefetch() for Buffered IO (experiment)
type: feature request
versions: Python 3.3, Python 3.4

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<http://bugs.python.org/issue12053>
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