[Zope] Temp Folder Magic

[Terry Hancock]

Chris McDonough wrote:
> There is a TemporaryFolder class in Zope.  It's in
> lib/python/Products/TemporaryFolder.py and its named
> MountedTemporaryFolder.  I recommend against subclassing
> MountedTemporaryFolder unless you want to spend the time to understand
> ZODB "mounting".

Actually, I got it working by inheriting from ObjectManager
and simply *containing* a Temporary Folder. I'm not sure if
that was strictly necessary, but I like it better this way
anyway (for one thing, it makes it possible to query the
cache independently of my __getattr__ overload which is one
of those "kids don't try this at home" techniques ;-D, so
its good to minimize the impact as much as possible).

> A temporary folder is an object that is a mount
> point.  It mounts a TemporaryStorage-backed database and masquerades as
> its root object.  When you traverse one of these things, the __of__
> method of the mount point object is called, and that returns the a
> Folder object that actually lives in another ZODB.  To understand it
> fully, you'd need to read the source of TemporaryFolder.py and
> MountPoint.py.  

Chris, I know "beggars can't be choosers", but seriously,
I think it would be a big improvement of the code to put
the above text into a nice sweet little comment block
inside TemporaryFolder.py. The existing comments are
inadequate (this is an amazing understatement).  It will
do exactly as you wrote it.

<rant>
Yes, it's open-source. Yes, no one is paying you for it.
So what?  You released it because you want it to be used
and improved. You want people to help you with it. You
want people to document it for you (also for free, I
might add).  And you don't really want to waste your
time answering the same questions over and over again.
So why are you shooting yourself in the foot by making
it difficult for them?  Comments are cheap, and a real
bargain in the long run.
</rant>

> But I honestly don't think using a TemporaryFolder for this is the right
> thing here.  Your object should return different images when different
> methods are called on it, and each method should have its own URL.  

Each image *does* get a separate URL. Downstream
caches can take advantage of this.  And yes, that's
why I did it that way.

Anyway I disagree on the design decision. No offense,
but I have to live with it, so I'll gamble on my own
judgement.

Anyway -- thanks for the description of how TemporaryFolder
is meant to work. And I guess you must be the author of
the module itself, in which case, thanks for that too,
it's a nice addition to Zope.

VarImage now passes my stress test, which is to ask
for a page with 300 different sizes of the same image
(this mainly tests the conflict problem that arises
when a single storage location is used). Cache
performance is good -- the second request for the
same page is very quick indeed (this tests the scaling
performance).

So I'm a happy camper. We'll have a copy on our
project site at Sourceforge sometime soon, if anyone
would like to use a freely-resizing image type in
Zope, we've found it quite useful in the design
process:

http://sourceforge.net/projects/spacelift

(I separated VarImage out into a separate product for
easier testing and because it's probably useful for more
than just Narya).

Thanks,
Terry


-- 
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Terry Hancock
hancock@anansispaceworks.com       
Anansi Spaceworks                 
http://www.anansispaceworks.com 
P.O. Box 60583                     
Pasadena, CA 91116-6583
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