py3k buffered IO - flush() required between read/write?

[Martin P. Hellwig]

On 11/05/2011 19:08, Genstein wrote:
> On 11/05/2011 19:24, Terry Reedy wrote:
>> 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.
>
> Thanks for a quick response. Perhaps I was being unclear - in py3k,
> given the following code and assuming no errors arise:
>
>  > f = open("foo", "w+b")
>  > f.write(b'test')
>  > f.seek(0)
>  > print(f.read(4))
>
> What is the printed result supposed to be?
>
> i) b'test'
> ii) never b'test'
> iii) platform dependent/undefined/other
>
> All the best,
>
> -eg.

from:
http://docs.python.org/py3k/library/functions.html#open
"""
open(file, mode='r', buffering=-1, encoding=None, errors=None, 
newline=None, closefd=True)¶
<cut>
buffering is an optional integer used to set the buffering policy. Pass 
0 to switch buffering off (only allowed in binary mode), 1 to select 
line buffering (only usable in text mode), and an integer > 1 to 
indicate the size of a fixed-size chunk buffer. When no buffering 
argument is given, the default buffering policy works as follows:

     * Binary files are buffered in fixed-size chunks; the size of the 
buffer is chosen using a heuristic trying to determine the underlying 
device’s “block size” and falling back on io.DEFAULT_BUFFER_SIZE. On 
many systems, the buffer will typically be 4096 or 8192 bytes long.
     * “Interactive” text files (files for which isatty() returns True) 
use line buffering. Other text files use the policy described above for 
binary files.
"""

So given that explanation, and assuming I understand it, I go for option 
'iii'.

-- 
mph