Re: How to catch a line with Popen
Chris Torek wrote: Since it is a generator that only requests another line when called, it should be fine Is it, then, that until the new itaration, the callee is on pause? -- goto /dev/null -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
Chris Torek wrote: In at least some versions of Python 2 I'm with P3k :P. However thank you for your guidelines. Last my attempt was to use a *for* p.wait() , as mentioned earlier That looks good enough. I noted some little delay for the first lines, mostly sure Popen assign some buffer even it is not set. Haven't you try a perpetual ping, how would be the line_at_a_time ? -- goto /dev/null -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
Chris Torek wrote: In at least some versions of Python 2 [the file-type object iterators behave badly with pipes] (This may still be true in Python 3, I just have no experience with Py3k. At least some version of Python 2 means the ones I have access to, and have tried. :-) ) In article is0d44$d7m$1...@speranza.aioe.org TheSaint nob...@nowhere.net.no wrote: I'm with P3k :P. However thank you for your guidelines. Last my attempt was to use a *for* p.wait() , as mentioned earlier If you have a process that has not yet terminated and that you must stop from your own python program, calling the wait() method will wait forever (because you are now waiting for yourself, in effect -- waiting for yourself to terminate the other process). The only time to call p.wait() (or p.communicate(), which itself calls the wait() method) is when you believe the subprocess is on its wao to terminating -- in this case, after you force it to do so. That looks good enough. I noted some little delay for the first lines, mostly sure Popen assign some buffer even it is not set. According to the documentation, the default buffer size of Python 2 is 0, which is passed to fdopen() and makes the resulting files unbuffered. I recall some sort of changes discussed for Py3k though. Haven't you try a perpetual ping, how would be the line_at_a_time ? Since it is a generator that only requests another line when called, it should be fine. (Compare to the itertools cycle and repeat generators, for instance, which return an infinite sequence.) -- In-Real-Life: Chris Torek, Wind River Systems Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) +1 801 277 2603 email: gmail (figure it out) http://web.torek.net/torek/index.html -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
Tim Roberts wrote: Are you specifying a buffer size in the Popen command? If not, then the Python side of things is unbuffered The buffer is as per default. The program reports one line around 1/2 second time. I think I'll look into the option as Nobody states: p = subprocess.Popen(...) for line in p.stdout: ... p.wait() It is strange that would take a for cycle, rather than catching the line on- the-fly. I can judge it now, I'm going to try it out. -- goto /dev/null -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
On Sun, May 29, 2011 at 3:02 AM, TheSaint nob...@nowhere.net.no wrote: Tim Roberts wrote: Are you specifying a buffer size in the Popen command? If not, then the Python side of things is unbuffered The buffer is as per default. The program reports one line around 1/2 second time. I think I'll look into the option as Nobody states: p = subprocess.Popen(...) for line in p.stdout: ... p.wait() It is strange that would take a for cycle, rather than catching the line on- the-fly. I can judge it now, I'm going to try it out. What do you mean by on-the-fly in this context? Cheers, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
Chris Rebert wrote: What do you mean by on-the-fly in this context I just suppose to elaborate the latest line, as soon it's written on the pipe, and print some result on the screen. Imaging something like p= Popen(['ping','-c40','www.google.com'], stdout=PIPE) for line in p.stdout: print(str(line).split()[7]) I'd like to see something like *time=54.4* This is just an example, where if we remove the -c40 on the command line, I'd expect to read the latest line(s), until the program will be killed. -- goto /dev/null -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
TheSaint wrote: I just suppose to elaborate the latest line, as soon it's written on the pipe, and print some result on the screen. I think some info is also here: http://alexandredeverteuil.blogspot.com/ -- goto /dev/null -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
In article irtj2o$h0m$1...@speranza.aioe.org
TheSaint nob...@nowhere.net.no wrote:
Chris Rebert wrote:
I just suppose to elaborate the latest line, as soon it's written on the
pipe, and print some result on the screen.
Imaging something like
p= Popen(['ping','-c40','www.google.com'], stdout=PIPE)
for line in p.stdout:
print(str(line).split()[7])
I'd like to see something like *time=54.4*
This is just an example, where if we remove the -c40 on the command line,
I'd expect to read the latest line(s), until the program will be killed.
In at least some versions of Python 2, file-like object next
iterators do not work right with unbuffered (or line-buffered)
pipe-file-objects. (This may or may not be fixed in Python 3.)
A simple workaround is a little generator using readline():
def line_at_a_time(fileobj):
Return one line at a time from a file-like object.
Works around the iter behavior of pipe files in
Python 2.x, e.g., instead of for line in file you can
write for line in line_at_a_time(file).
while True:
line = fileobj.readline()
if not line:
return
yield line
Adding this to your sample code gives something that works for me,
provided I fiddle with it to make sure that the only lines
examined are those with actual ping times:
p = subprocess.Popen([ping, -c5, www.google.com],
stdout = subprocess.PIPE)
for lineno, line in enumerate(line_at_a_time(p.stdout)):
if 1 = lineno = 5:
print line.split()[6]
else:
print line.rstrip('\n')
p.wait() # discard final result
(Presumably the enumerate() trick would not be needed in whatever
you really use.)
--
In-Real-Life: Chris Torek, Wind River Systems
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) +1 801 277 2603
email: gmail (figure it out) http://web.torek.net/torek/index.html
--
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How to catch a line with Popen
Hello. I'm looking into subprocess.Popen docs. I've launch the program with its arguments and that's smooth. I'm expecting to read the output by *comunicate()* at every line that prgram may blow during the process, but the output is given only when the child process is ended. I'd like to process the lines to display an information in percentage during the running time of the child. Sorry but I'm poor of know-how, so I'm stuck over to find a clue. -- goto /dev/null -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
On Sun, 29 May 2011 00:01:56 +0800, TheSaint wrote: I'm looking into subprocess.Popen docs. I've launch the program with its arguments and that's smooth. I'm expecting to read the output by *comunicate()* at every line that prgram may blow during the process, but the output is given only when the child process is ended. .communicate() reads until EOF, .wait()s for the process to terminate, then returns the output as a pair of strings. If you want to read data while the process is running, use the process' .stdout and/or .stderr members, e.g.: p = subprocess.Popen(...) for line in p.stdout: ... p.wait() Don't forget to .wait() on the process when you're done, regardless of whether you actually need the exit code. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
TheSaint nob...@nowhere.net.no wrote: I'm looking into subprocess.Popen docs. I've launch the program with its arguments and that's smooth. I'm expecting to read the output by *comunicate()* at every line that prgram may blow during the process, but the output is given only when the child process is ended. I'd like to process the lines to display an information in percentage during the running time of the child. Are you specifying a buffer size in the Popen command? If not, then the Python side of things is unbuffered. It's possible that the application you are launching is buffering its output, so that it doesn't SEND until the application ends. -- Tim Roberts, t...@probo.com Providenza Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to catch a line with Popen
On Sat, May 28, 2011 at 4:32 PM, Tim Roberts t...@probo.com wrote: TheSaint nob...@nowhere.net.no wrote: I'm looking into subprocess.Popen docs. I've launch the program with its arguments and that's smooth. I'm expecting to read the output by *comunicate()* at every line that prgram may blow during the process, but the output is given only when the child process is ended. I'd like to process the lines to display an information in percentage during the running time of the child. Are you specifying a buffer size in the Popen command? If not, then the Python side of things is unbuffered. It's possible that the application you are launching is buffering its output, so that it doesn't SEND until the application ends. I believe there are 4 normal ways, and 1 special way of getting output from a buffered application: 1) As you mentioned, the program could terminate 2) Also, the program could just have written enough to fill its buffer, so it outputs the content of the buffer before starting to fill it again 3) Also, the program could call flush 4) Also, the program could use an unbuffered file, like stderr - not all file in an application are astonishingly likely to be buffered the same way And the special one: 1) Sometimes you can take a buffered program and get it to be unbuffered (or at least line buffered) by running it on a pty. -- http://mail.python.org/mailman/listinfo/python-list
