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
