[issue11633] regression: print buffers output when end=''
anatoly techtonik techto...@gmail.com added the comment: I've tried to switch to Python 3 once more and stumbled upon this problem once more. Seems like this regression got stale. Last Victor's proposal seems reasonable for me. Should we open a new, more clear bug report and close this one? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
Terry J. Reedy tjre...@udel.edu added the comment: No, I don't think so. Another issue will not magically create more time for anyone. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
anatoly techtonik techto...@gmail.com added the comment: On Mon, Jan 9, 2012 at 2:03 PM, Terry J. Reedy rep...@bugs.python.orgwrote: Terry J. Reedy tjre...@udel.edu added the comment: No, I don't think so. Another issue will not magically create more time for anyone. But anyone will waste less time to get to the outcome of discussion. -- anatoly t. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
STINNER Victor victor.stin...@haypocalc.com added the comment:
amaury When python is run from a console, sys.stdout is line buffered.
amaury sys.stdout.write() flushes if there is a carriage return.
amaury No need to change anything here.
Anatoly would like a flush after all calls to print().
print() could call file.flush() if file.isatty(), *after* the multiple
calls to file.write().
I vote +0 to change print(), call sys.stdout.flush(), if:
- file option is not used (and so, sys.stdout is used)
- sys.stdout is a TTY
- end option is used (fast heuristic to check if print will write a newline or
not, a better one whould be to check if end contains a newline character or
not, but we had to check for \n and/or \r, for a little gain)
But I don't want to change print() for print(text, file=file), because it would
make Python slower and print(... file=file) is not used to an interactive
prompt or to display informations to the user.
Behavior is same when pasting into interactive interpreter ...
I presume interpreter flushes before or after printing next prompt.
Did you wrote all commands on the same line? Python does change stdout buffer
in interactive mode:
if (Py_UnbufferedStdioFlag) {
#ifdef HAVE_SETVBUF
setvbuf(stdin, (char *)NULL, _IONBF, BUFSIZ);
setvbuf(stdout, (char *)NULL, _IONBF, BUFSIZ);
setvbuf(stderr, (char *)NULL, _IONBF, BUFSIZ);
#else /* !HAVE_SETVBUF */
setbuf(stdin, (char *)NULL);
setbuf(stdout, (char *)NULL);
setbuf(stderr, (char *)NULL);
#endif /* !HAVE_SETVBUF */
}
else if (Py_InteractiveFlag) {
#ifdef MS_WINDOWS
/* Doesn't have to have line-buffered -- use unbuffered */
/* Any set[v]buf(stdin, ...) screws up Tkinter :-( */
setvbuf(stdout, (char *)NULL, _IONBF, BUFSIZ);
#else /* !MS_WINDOWS */
#ifdef HAVE_SETVBUF
setvbuf(stdin, (char *)NULL, _IOLBF, BUFSIZ);
setvbuf(stdout, (char *)NULL, _IOLBF, BUFSIZ);
#endif /* HAVE_SETVBUF */
#endif /* !MS_WINDOWS */
/* Leave stderr alone - it should be unbuffered anyway. */
}
#ifdef __VMS
else {
setvbuf (stdout, (char *)NULL, _IOLBF, BUFSIZ);
}
#endif /* __VMS */
(it doesn't check if stdout is a TTY or not, but I don't think that it is very
useful to use the interactive mode outside a TTY)
I have always experienced and expected Python's print to screen
to be immediately visible. I thought that was pretty standard
in other languages with a print-to-screen separate from
general file-write.
Did you try Perl, Ruby, bash and other languages? I know that at least the C
language requires an explicit call to fflush(stdout). I always used that.
Terry, IDLE is completely different, its sys.stdout completely
bypasses the new io stack, and there is no buffering...
As I wrote: unbuffered mode is not implemented for TextIOWrapper. So even
with python3 -u, sys.stdout.write(abc) doesn't flush immediatly into the
underlying FileIO.
--
___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue11633
___
___
Python-bugs-list mailing list
Unsubscribe:
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
Terry J. Reedy tjre...@udel.edu added the comment: I completely agree that file/socket output should be left alone. Flushing char by char to either is a bit insane. The two interactive to screen use cases I can think of are text progress meters, mentioned by Anatoly, such as : Working (1 dot printed at intervals) and timed text like import time for c in 'Similated 10 cps teletype output': print(c,end='') time.sleep(.1) print() which works fine from IDLE and whose non-functioning when started otherwise would puzzle any beginner and many beyond. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
New submission from anatoly techtonik techto...@gmail.com: print() function for some reason buffers output on Windows if end!='\n'. In attached examples Processing.. string is shown in Python 3.2 only after the actual processing is finished, while in Python 2.6 it is shown before. -- files: printtest3.py messages: 131736 nosy: techtonik priority: normal severity: normal status: open title: regression: print buffers output when end='' versions: Python 3.2 Added file: http://bugs.python.org/file21333/printtest3.py ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
Changes by anatoly techtonik techto...@gmail.com: Added file: http://bugs.python.org/file21334/printtest2.py ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
STINNER Victor victor.stin...@haypocalc.com added the comment: printtest2.py displays directly Processing.. on Windows, but not on Linux. It looks like stdout is not buffered on Windows, which looks like a bug to bug :-) I think that it is safer to always call sys.stdout.flush() to ensure that your message is directly displayed. With Python 2, you can use -u flag (unbuffered output) to avoid the explicit flush, but this is very inefficient (slow). Python 3 uses line buffers, even with python3 -u, for better performances. If you want to see directly Processing.. , as Python 2, call sys.stdout.flush(). It is not a regression, it is a choice to be efficient. -- nosy: +haypo resolution: - invalid status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
anatoly techtonik techto...@gmail.com added the comment: From my perspective it is a regression on Windows and a bug in Linux version of Python 2.x, which unfortunately can not be fixed, because of 2.x release process. If the fact that print statement doesn't output anything when called is not a bug - then should be documented long ago. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
STINNER Victor victor.stin...@haypocalc.com added the comment: From my perspective it is a regression on Windows and a bug in Linux version of Python 2.x, which unfortunately can not be fixed, because of 2.x release process. Line buffering is used by default on most operating systems (ok, maybe not Windows, which looks strange to me) and is not specific to Python. Yes, Python has subtle differences on different operating systems, but at least it looks like Python 3 has the same behaviour on Linux and Windows ;-) If the fact that print statement doesn't output anything when called is not a bug - then should be documented long ago. Can you please write a patch for the doc? Reopen the issue if you have a patch. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
anatoly techtonik techto...@gmail.com added the comment: How about making print() user-friendly with flushing after every call, and if you want explicitly want speed - use buffered sys.stdout.write/flush()? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
STINNER Victor victor.stin...@haypocalc.com added the comment: How about making print() user-friendly with flushing after every call, and if you want explicitly want speed - use buffered sys.stdout.write/flush()? This is exactly the -u option of Python 2: use it if you would like a completly unbuffered sys.stdout in a portable way. In Python 3, it is only useful to flush at each line, even if the output is not a console, but a pipe (e.g. output redirected to a file). But nobody asked yet to have a fully unbuffered sys.stdout in Python 3. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
anatoly techtonik techto...@gmail.com added the comment: You must realize that the most common use case for print(..., end!='\n') is when you want to notify user about intermediate progress of a very long operation. Making documentation for simple print() statement overloaded with low level buffering details makes language seem overly complicated for new users. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
Amaury Forgeot d'Arc amaur...@gmail.com added the comment: We are talking about different things here: - When python is run from a console, sys.stdout is line buffered. sys.stdout.write() flushes if there is a carriage return. No need to change anything here. - print() could call file.flush() if file.isatty(), *after* the multiple calls to file.write(). -- nosy: +amaury.forgeotdarc ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
Terry J. Reedy tjre...@udel.edu added the comment: Python 3.2, WinXP, IDLE edit window, F5 Run: 'Processing ...' appears immediately, 'Done' 3 sec later. The only difference between printtest2/3 is where 'Done' appears. Behavior is same when pasting into interactive interpreter -- has to be since the first two prints are executed before the sleep. I presume interpreter flushes before or after printing next prompt. IDLE must do same even when running from editor even when not printing prompts. Anatoly, I gather you ran files by some other method. I disagree with closing this yet. Print was designed to be a simplified wrapper around sys.stdout.write (and now, any file.write). Requiring that one import sys to use print goes against that. I have always experienced and expected Python's print to screen to be immediately visible. I thought that was pretty standard in other languages with a print-to-screen separate from general file-write. When printing to screen, efficiency is, I believe, a non-issue. Writing to files or the net is a whole different ballgame. Amaury's idea of checking isatty seems good. Otherwise, print should gain an optional, no-default flush=True/False parameter (no default because behavior currently varies.) Until then, non-flushing *should* be documented. The current doc for print does not seem to address the issue either way. Amaury, I though 'run from console' more or less meant 'isatty', so I am not sure I understand your comment. -- assignee: - docs@python components: +Documentation, Library (Lib) nosy: +docs@python, terry.reedy resolution: invalid - status: closed - open type: - feature request versions: +Python 3.3 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
Amaury Forgeot d'Arc amaur...@gmail.com added the comment: The attached patch calls if file.isatty(): file.flush() at the end of the print function: - only when an end argument was specified - errors in file.isatty() are ignored (and then no flush occurs) -- keywords: +patch Added file: http://bugs.python.org/file21349/print-flush.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
Amaury Forgeot d'Arc amaur...@gmail.com added the comment: Python 3.2, WinXP, IDLE edit window, F5 Run: 'Processing ...' appears immediately, 'Done' 3 sec later. Terry, IDLE is completely different, its sys.stdout completely bypasses the new io stack, and there is no buffering... -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue11633] regression: print buffers output when end=''
Changes by Éric Araujo mer...@netwok.org: -- assignee: docs@python - components: +Interpreter Core -Documentation, Library (Lib) keywords: +3.2regression nosy: +georg.brandl -docs@python ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue11633 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
