[issue10144] Buffering bug after calling curses function

[Ned Deily]

Changes by Ned Deily :


--
resolution:  -> wont fix
status: open -> closed

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[issue10144] Buffering bug after calling curses function

[Fernando Perez]

Fernando Perez  added the comment:

No problem for us (IPython) if you mark it as won't fix. I've just applied the 
environment workaround you guys suggested:

http://github.com/ipython/ipython/commit/147b245d2ead0e15d2c17b7bb760a03126660fb7

Thanks a lot for that tip!  That leaves us in good shape.

--
nosy: +fperez

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[issue10144] Buffering bug after calling curses function

[Ned Deily]

Ned Deily  added the comment:

Thanks for NCURSES_NO_SETBUF ("when it doubt read the man page"!).  Since the 
problem does not seem to exist in python3 and this is likely been an issue for 
a long time and apparently not previously reported and there are various 
workarounds, I think this could be closed as "wont fix".  Any objections?

--

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[issue10144] Buffering bug after calling curses function

[Andreas Stührk]

Andreas Stührk  added the comment:

That behaviour is indeed caused by ncurses as it changes the buffer size of 
stdio. The rationale behind that is explained in a comment in 
ncurses/tinfo/setbuf.c 
(http://codesearch.google.com/codesearch/p?hl=en#5KTrgOW2hXs/pub/nslu2/sources/ncurses-5.4.tar.gz%7CqZkYBenqdbw/ncurses-5.4/ncurses/tinfo/setbuf.c&l=46)

That behaviour is also mentioned in the man-page of ncurses and one can disable 
it using the NCURSES_NO_SETBUF environment variable. If I set that environment 
variable, the example behaves as expected on my machine.

--
nosy: +Trundle

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[issue10144] Buffering bug after calling curses function

[Ned Deily]

Ned Deily  added the comment:

The problem is reproducible with the python2 versions I have access to, that 
is, on Mac OS X and Debian Linux, and likewise not with any of the python3 3.1 
and 3.2 versions.  It is most likely due to the underlying ncurses library 
interacting with the libc stdio, maybe changing the buffer size of the stdout 
file. The output is flushed as expected if the program is changed to use the 
python2.7 io module to write to stdout, like python3 does, rather than print 
which uses the 'file' object.  As a workaround on python2, it looks like the 
expected behavior can be restored by closing and reopening sys.stdout with 
something like this:

   f()
   stdout=sys.stdout
   print('Calling bug() now!')
   bug()
   fn = sys.stdout.fileno()
   sys.stdout.close()
   sys.stdout = os.fdopen(fn,'a')
   f()

--
nosy: +akuchling, ned.deily, pitrou
versions:  -Python 2.6

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[issue10144] Buffering bug after calling curses function

[Wes McKinney]

New submission from Wes McKinney :

We tracked a bug originating in IPython to the Python interpreter itself, seems 
to be present in 2.6.x and 2.7.x but not 3.1.x. This is on Ubuntu Linux 10.04, 
does not seem to occur in OS X 10.6.

Reference: http://article.gmane.org/gmane.comp.python.ipython.user/5336

> cat bufferbug.py
"""Strange bug in buffering of sys.stdout after calling curses functions.
"""
import time
import curses

def bug():
   curses.initscr()
   curses.endwin()

def f(n=2):
   s = 0.75
   for i in range(n):
   print i
   time.sleep(s)
   print i+1

if __name__ == '__main__':
   f()
   print 'Calling bug() now!'
   bug()
   f()



--
components: Interpreter Core
messages: 119115
nosy: Wes.McKinney
priority: normal
severity: normal
status: open
title: Buffering bug after calling curses function
type: behavior
versions: Python 2.6, Python 2.7

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