[Zope-dev] A Modest Proposal Concerning Monkey Patches

[Jim Penny]

On Wed, Aug 14, 2002 at 08:46:41AM +0100, Adrian Hungate wrote:
> >
> > Again, monkey patching doesn't modify source code, so I don't know
> > what would be getting written into tmp.
> >
> > > Comments?
> >
> > Didn't someone else make a proposal (with code) to handle this?
> > Was it PatchKit?
> 
> Yup, and it is more than a proposal, it is a full blown product (
> http://www.zope.org/Members/haqa/PatchKit ) with some patches already in it
> (They can be removed if you wish).

Nope... we have been down this path before.  Note this what I need (see
below on why) requires modification, and not simple replacement, of
whatever code is currently running.  As far as I can see, Patchkit does 
nothing to make this possible.

The problem is that A) monkey patches may or may not
have been applied before a given product sees anything, and B)  there is
no reasonable way to discover what (or even if) patches have been
applied by other products.

If you are going to go down the monkeypatch path, then there needs to be
some way for other monkeypatchers to discover what you have done, so
that they can decide if they can 1)  extend your code to be compatible
with theirs, 2) refuse to install their code, or 3)  blow your
pre-existing code away.

Current monkeypatch code always does 3.  Patchkit has, as far as I can
tell no way to make 1 or 2 easier.  It just makes it easier to blow
other people's work away!

Background:  I am debian maintainer for zope-zshell.  The debian release
is currently a version behind.  I have been holding off updating it 
because I would like the ZMI box.  I cannot modify manage_main.py directly,
because it belongs to the zope package and the changes would be blown
away on any upgrade of zope.  I was starting to turn it into a python
product, but zope-externaleditor has been packaged, and it monkeypatches
manage_main.  The naive thing to do would be to install it as a
monkeypatch.  But then, either I blow away externaleditor, or
externaleditor blows away zshell, depending on the order in which zope
installs products on startup.  There are several other products that
monkeypatch manage_main as well, building a nice mutual destruction
club.

Jim Penny

PS:  I would also like to hear general responses to Jerome's proposal.
Clearly this was not an API, no arguments have been specified.  But is
there a general consensus that this is a reasonable thing to do?
Please, if it isn't to late, could we make it a 2.6 thing?

> 
> There is a fledgling API, though I probably need to document it better, make
> some unit tests etc, but it is there, and it works (For me... YMMV).
> 
> > But yes, some "standard" would be helpful, possibly with supporting
> > utilities, to allow multiple monkeypatches coexist, I think.
> >
> > On the other hand, in Zope3 you just change the zcml files...although
> > I think there was a discusion of an analogous issue there (coexistence
> > of multiple "modifications" to the same area) and I'm not sure
> > a conclusion was reached (but I can't remember for sure).
> >
> 
> Adrian...
> 
> --
> Adrian Hungate
> EMail: adrian@haqa.co.uk
> Web: http://www.haqa.co.uk
> 
>