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Newsgroups: comp.lang.python
Date: Fri, 8 Feb 2013 09:09:31 -0800 (PST)
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Subject: Re: Monitoring updating directory for image for GUI
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Xref: csiph.com comp.lang.python:38465



> Who/what are you responding to here? You haven't included any context
> from what you're replying to.

Sorry, never really used Google Groups, or anything like this before. That =
I was responding to only Chris Angelico with his question of how real-time =
it needed to be...since it takes some time for Lilypond to create the image=
s.


> So you have a thread that updates the image and then checks the stack
> to see if a new image is available? Can you not just have it only try
> to load the newest image?

That is what I am trying to figure out how to do. I have a counter that upd=
ates with every note that is grabbed from the stream. That counter is passe=
d into a threaded class that might or might not create the image right away=
...but seems to create them sequentially from what I have seen so far (I do=
n't know if that is absolute thought).=20

Please let me know you thought on the above part! Each new thread should on=
ly take only a very small amount longer to do than the previous thread that=
 was started...because it has one more note to deal with this time.

Anyways...I do have the count of the latest image that WILL BE created...bu=
t by the time that one is created in the directory, a new note is most like=
ly streamed in and replaces that count. Therefore, I cannot really do that.=
..I think.

hmmmm, I wonder. I create the images via OS command that will .wait() on a =
subprocess.Popen(). I could increment the counter there? Or do something th=
ere that will let me know of the most recent image file via a counter or so=
mething? But it needs to be thread-safe

> You say that you control the filenames of the images. I assume that
> you are notified when a file is created and given the filename of the
> new file. So you can maintain a mapping of filename->ordering. In this
> case you can determine when a file notification arrives whether the
> filename corresponds to a more recent note than the filename that is
> currently waiting to be displayed (or is currently displayed). If it
> is an older note then discard it (and delete the file?) when the
> notification arrives. If it is newer then discard the one that is
> currently waiting to be displayed. This way there are always either
> zero or one filenames waiting and if there is one then it is the most
> recent one seen so far.

I am not notified when the file is created...but like I said before, I wait=
 on the subprocess and could do something there.

> Is that using something like watchdog?
> http://pypi.python.org/pypi/watchdog

I don't know about Watchdog...but from an earlier version of a tutorial onl=
ine...

http://pypi.python.org/pypi/watchdog/0.3.6  (Yes, it is currently on v0.6.0=
 and this is older - v0.3.6)

... it looks like I COULD do something like...

class MyEventHandler(FileSystemEventHandler):
    ...
    ...
    def on_created(self, event):
        # update gtkImage object here!!

...right? Or no? I will say that I kind of like that. The only thing is, do=
 you think that would "flicker" in the GUI if a bunch of new images are cre=
ated in quick succession? Anyways, I think that would be the most desired o=
utcome...with every image being used and replaced with something newer with=
out a large lag...as it will happen during each creation of a new image.=20


> It matters for how you monitor the directory at least.

My other question, if I do monitor the directory vs. use a queue, or stack =
/ list, is how to monitor a directory that is actively being updated while =
I search for the file. This might not matter and something like os.walk() m=
ight work...I don't know, I don't know python that well yet.

Do you get what I mean with this?


Sorry if something seems out of place...I was going back and forth and addi=
ng / removing things to my reply.

Thanks,
Christopher