New submission from Genstein <python...@genstein.net>:
Reporting this as requested by Antoine Pitrou: Under certain circumstances in
Python 3.2 (r32:88445) it's possible for buffered I/O to lose data before it is
written and/or return the wrong results when reading. I tripped over this issue
whilst writing an assembler which first writes out a bunch of binary data and
then goes back over it in a somewhat arbitrary order patching addresses.
The following code demonstrates the issue:
[code]
START = 0
MID = 1
LENGTH = 4
def test(buffering):
f = open("test.bin", "w+b", buffering = buffering)
for i in range(LENGTH):
f.write(b'\x00')
f.seek(MID)
f.read(1)
f.write(b'\x00')
f.seek(MID)
f.write(b'\x01')
f.seek(START)
f.seek(MID)
print(f.read(1))
f.close()
print("Buffered result: ")
test(-1)
print("Unbuffered result:")
test(0)
[end code]
Output on both Gentoo and Vista is:
Buffered result:
b'\x00'
Unbuffered result:
b'\x01'
Expected output is b'\x01' in both cases.
The issue is reproducible with larger files provided that the constants are
increased ~proportionally (START 0, MID 500, LENGTH 1000 for example).
Transposing the buffered/unbuffered tests and/or using different buffer sizes
for the buffered test seem have no effect.
The lengthy code at this URL also demonstrates the issue:
http://pastebin.com/xqrzKr5D The above was produced from this code, which was
autogenerated by intercepting my assembler's output.
----------
components: IO
messages: 135830
nosy: genstein
priority: normal
severity: normal
status: open
title: Buffered I/O inconsistent with unbuffered I/O in certain cases
type: behavior
versions: Python 3.2
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue12062>
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