Bug 3.11.x behavioral, open file buffers not flushed til file closed.

[aapost]

I have run in to this a few times and finally reproduced it. Whether it 
is as expected I am not sure since it is slightly on the user, but I can 
think of scenarios where this would be undesirable behavior.. This 
occurs on 3.11.1 and 3.11.2 using debian 12 testing, in case the 
reasoning lingers somewhere else.

If a file is still open, even if all the operations on the file have 
ceased for a time, the tail of the written operation data does not get 
flushed to the file until close is issued and the file closes cleanly.

2 methods to recreate - 1st run from interpreter directly:

f = open("abc", "w")
for i in range(50000):
   f.write(str(i) + "\n")

you can cat the file and see it stops at 49626 until you issue an f.close()

a script to recreate:

f = open("abc", "w")
for i in range(50000):
   f.write(str(i) + "\n")
while(1):
   pass

cat out the file and same thing, stops at 49626. a ctrl-c exit closes 
the files cleanly, but if the file exits uncleanly, i.e. a kill command 
or something else catastrophic. the remaining buffer is lost.

Of course one SHOULD manage the closing of their files and this is 
partially on the user, but if by design something is hanging on to a 
file while it is waiting for something, then a crash occurs, they lose a 
portion of what was assumed already complete...