On 5/11/2011 12:27 PM, Genstein wrote:
In py3k is it necessary to flush() a file between read/write calls in order
to see consistent results?
I ask because I have a case under Python 3.2 (r32:88445) where it does
appear to be, on both Gentoo Linux and Windows Vista.
I've naturally read http://docs.python.org/py3k/library/io.html and
http://docs.python.org/py3k/tutorial/inputoutput.html#reading-and-writing-files
but could find no reference to such a requirement.
PEP 3116 suggested this might not be required in py3k and the
implementation notes in bufferedio.c state "BufferedReader,
BufferedWriter and BufferedRandom...share a single buffer...this enables
interleaved reads and writes without flushing." Which seemed conclusive
but I'm seeing otherwise.
I have a test case, which is sadly rather long:
http://pastebin.com/xqrzKr5D It's lengthy because it's autogenerated
from some rather more complex code I'm working on, in order to reproduce
the issue in isolation.
I notice that you have required seek calls when switching between
writing and reading. If you want others to look at this more, you should
1) produce a minimal* example that demonstrates the questionable
behavior, and 2) show the comparative outputs that raise your question.
The code is way too long to cut and paste into an editor and see what is
does on my windows machine.
*minimal = local minimum rather than global minimum. That means that
removal or condensation of a line or lines removes the problem. In this
case, remove extra seeks, unless doing so removes behavior discrepancy.
Condense 1 byte writes to multibyte writes, unless ... . Are repeated
interleavings required or is write, seek, read, seek, write enough?
--
Terry Jan Reedy
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