[PyQt] QFileSystemWatcher triggering too many signals

[Lars Beiderbecke]

Hello,

I'm trying to watch a file for changes using QFileSystemWatcher:

class MainWindow(QtGui.QMainWindow):

    def __init__(self,parent,args=None):
        QtGui.QMainWindow.__init__(self)
        self.count = 0
        self.watcher = QtCore.QFileSystemWatcher();
        self.watcher.addPath("myfile");
        self.connect(self.watcher, QtCore.SIGNAL("fileChanged(const
QString&)"), self.check)

    def check(self, file = "*"):
        self.count += 1
        print "Modified:", str(file), " #", self.count

This works, more or less, as for every

$ touch myfile

I get exactly one invocation of check().  If the changes are larger,
however, I get an excessive amount of invocations.  Some examples:

$ dd if=/dev/urandom of=sample bs=1k count=100
$ cp sample myfile
-> 4 invocations
$ vi myfile  # replacing first char, then :wq
-> 21 invocations
$ joe myfile  # ditto
-> 11 invocations
$ touch myfile
-> 1 invocations
$ cat sample > watched
-> 3 invocations
$ cat sample sample > watched
-> 6 invocations

Now I realize that editors may do weird things to files, but cp and
cat? Is this behavior considered normal?

System info: Ubuntu Precise, Linux kernel 3.2.0-36 x86_64, Python
2.7.3, PyQt 4.9.1 (?)

Regards
Lars