Re: [PyQt] graphical file tail

[Eric Frederich]

Thanks for the suggestions.  Unfortunately I do need to use Qt 4.6.2 from
RHEL 6.  This will also be on an NFS mounted drive.

This is for a GUI that monitors the output of jobs run on Sun Grid Engine
(SGE).  So its not that the files _happen_ to be on NFS, it's actually
_required_ that they are :-(

Any Qt4 help would be appreciated.
Am I cleaning up my tail processes correctly?  Is it just the QThreads I'm
screwing up?  Are there other hidden dangers with my implementation?
On Jun 24, 2013 7:25 PM, "John Lee"  wrote:

> On Mon, 24 Jun 2013, Eric Frederich wrote:
>
>  I'm trying to tail several files graphically.
>> I have been trying to find a way to tail several files in a GUI
>> without much luck at all.
>> I get errors from tail saying broken pipe.
>> I get PyQt errors saying underlying C++ objects have been destroyed.
>> I get other Qt errors saying that threads are still running when the
>> application exits
>> etc
>>
>> The implementation posted below seems to suffer from the following errors.
>> Not all the time.  It depends.
>>
>> QThread: Destroyed while thread is still running
>> QWaitCondition::wakeAll(): mutex lock failure:
>>
>
> You're not calling .wait on the threads, and you probably want to give
> e.g. your QObjects a parent where you can, so that Qt manages the lifetime
> of the wrapped C++ objects (e.g. pass in self to the parent arg of the
> QTextBrowser constructor).
>
> But, I recommend doing it a different way: I find event-based code easier
> to think about than threads.  So, if you can use Qt5, you might want to do
> away with the threads and the tail subprocess and replace them with
> QFileSystemWatcher.  Use event-based code instead of the threads (I'm not
> talking about Qt events, I just mean hook up to the signals that that class
> emits and process a little input at a time so as to avoid blocking the UI,
> using QTimer where needed).  I say Qt5 because Qt4 isn't very friendly to
> this way of working since it uses threads in the implementation of
> QFileSystemWatcher.
>
> Caveat: QFileSystemWatcher still has its problems, but the ones discussed
> at the URL below are more convenience issues than fundamental problems: I
> just found I had to experiment a bit to see when the different signals got
> emitted.
>
> http://blog.rburchell.com/**2012/03/qt-51-aka-when-**
> qfilesystemwatcher-might.html
>
> Caveat #2: I imagine QFileSystemWatcher does not support filesystems like
> NFS, at least on Linux kernels with inotify support (but don't take my word
> for it, check the source).
>
>
> John
> __**_
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>
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Re: [PyQt] graphical file tail

[John Lee]

On Mon, 24 Jun 2013, Eric Frederich wrote:


I'm trying to tail several files graphically.
I have been trying to find a way to tail several files in a GUI
without much luck at all.
I get errors from tail saying broken pipe.
I get PyQt errors saying underlying C++ objects have been destroyed.
I get other Qt errors saying that threads are still running when the
application exits
etc

The implementation posted below seems to suffer from the following errors.
Not all the time.  It depends.

QThread: Destroyed while thread is still running
QWaitCondition::wakeAll(): mutex lock failure:


You're not calling .wait on the threads, and you probably want to give 
e.g. your QObjects a parent where you can, so that Qt manages the lifetime 
of the wrapped C++ objects (e.g. pass in self to the parent arg of the 
QTextBrowser constructor).


But, I recommend doing it a different way: I find event-based code easier 
to think about than threads.  So, if you can use Qt5, you might want to do 
away with the threads and the tail subprocess and replace them with 
QFileSystemWatcher.  Use event-based code instead of the threads (I'm not 
talking about Qt events, I just mean hook up to the signals that that 
class emits and process a little input at a time so as to avoid blocking 
the UI, using QTimer where needed).  I say Qt5 because Qt4 isn't very 
friendly to this way of working since it uses threads in the 
implementation of QFileSystemWatcher.


Caveat: QFileSystemWatcher still has its problems, but the ones discussed 
at the URL below are more convenience issues than fundamental problems: I 
just found I had to experiment a bit to see when the different signals got 
emitted.


http://blog.rburchell.com/2012/03/qt-51-aka-when-qfilesystemwatcher-might.html

Caveat #2: I imagine QFileSystemWatcher does not support filesystems like 
NFS, at least on Linux kernels with inotify support (but don't take my 
word for it, check the source).



John
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[PyQt] Kled module

[Phil]

Thank you for reading this.

I'd like to include a led in my project which I've done in the past with 
Qt creator and Designer under C++. Adding the following to my Python 
project fails because there is no module named Kled.


self.kled = KLed(self.centralwidget)

Is it possible to add a Kled to a PyQt project?

--
Regards,
Phil
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Re: [PyQt] PyQt5 installation

[Phil Thompson]

On Mon, 24 Jun 2013 19:09:01 +0200, Detlev Offenbach
 wrote:
> Hello,
> 
> I just installed PyQt5 from source on openSUSE and 
> noticed, that the pyuic5 executable (script) didn't get 
> installed with executable rights. Did I do anything wrong?

No, it's a Linux specific bug. I was trying to avoid a warning message
when stripping a shell script.

Phil
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[PyQt] ANN: PyQtChart v1.3 Released

[Phil Thompson]

PyQtChart v1.3 has been released. This supports the new features of Qt
Charts v1.3.0. See...

http://blog.qt.digia.com/blog/2013/06/19/qt-charts-1-3-0-released-2/

It can be built against PyQt4 and PyQt5.

Phil
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[PyQt] graphical file tail

[Eric Frederich]

I'm trying to tail several files graphically.
I have been trying to find a way to tail several files in a GUI
without much luck at all.
I get errors from tail saying broken pipe.
I get PyQt errors saying underlying C++ objects have been destroyed.
I get other Qt errors saying that threads are still running when the
application exits
etc

The implementation posted below seems to suffer from the following errors.
Not all the time.  It depends.

QThread: Destroyed while thread is still running
QWaitCondition::wakeAll(): mutex lock failure:

Please tell me what I'm doing wrong.
Feel free to tell me if I'm doing something bone-headed.
Basically, I want to graphically tail files and when the GUI closes
the tail subprocesses are killed.
Seems like a simple request, but I can't get it right.

#!/usr/bin/env python

from PyQt4.QtCore import *
from PyQt4.QtGui import *

import os
from subprocess import Popen, PIPE

class Tailer(QThread):

def __init__(self, fname, parent=None):
super(Tailer, self).__init__(parent)
self.fname = fname
self.connect(self, SIGNAL('finished()'), self.cleanup)

def cleanup(self):
print 'CLEANING UP'
self.p.kill()
print 'killed'

def run(self):
command = ["tail", "-f", self.fname]
print command
self.p = Popen(command, stdout=PIPE, stderr=PIPE)
while True:
line = self.p.stdout.readline()
self.emit(SIGNAL('newline'), line.rstrip())
if not line:
print 'BREAKING'
break

def foo(self):
self.p.kill()

class TailWidget(QWidget):
def __init__(self, fnames, parent=None):
super(TailWidget, self).__init__(parent)
layout = QGridLayout()
self.threads = {}
self.browsers = {}
for i, fname in enumerate(fnames):
if not os.path.exists(fname):
print fname, "doesn't exist; creating"
p = Popen(['touch', fname], stdout=PIPE, stderr=PIPE)
out, err = p.communicate()
ret = p.wait()
assert ret == 0
t = Tailer(fname, self)
self.threads[fname] = t
b = QTextBrowser()
self.browsers[fname] = b
layout.addWidget(QLabel('Tail on %s' % fname), 0, i)
layout.addWidget(b, 1, i)
self.connect(t, SIGNAL("newline"), b.append)
t.start()
self.setLayout(layout)

def closeEvent(self, event):
for fname, t in self.threads.items():
t.foo()

if __name__ == '__main__':
import sys
app = QApplication(sys.argv)
tw = TailWidget(sys.argv[1:])
tw.show()
sys.exit(app.exec_())
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[PyQt] PyQt5 installation

[Detlev Offenbach]

Hello,

I just installed PyQt5 from source on openSUSE and 
noticed, that the pyuic5 executable (script) didn't get 
installed with executable rights. Did I do anything wrong?

Regards,
Detlev-- 
*Detlev Offenbach*
det...@die-offenbachs.de
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