[mod_python] Re: persistent, reliable globals

Ben ben at medianstrip.net
Mon Mar 8 19:52:55 EST 2004

Hello all,

After grovelling mod_python, mod_perl, and Apache API docs, what i've
discovered is this:

If you just want to initialize a global variable, you can probably do
that using the "PythonImport" directive.  in short:

ServerName foo.com
PythonPath "sys.path+['/path/to/MyGlobals']"
PythonImport MyGlobals foo.com

or something like this, depending on how you set the
PythonInterpPerDirective/Directory settings.  PythonImport happens
per-subinterpreter (not for the main interpreter, nor per-thread),
inside of the apache per-child hook.  This of course will only be
shared within a child process, within a named subinterpreter.  There
are good docs on how it is used in the mod_python manuals.

More examples:

<Directory /mydir>
	AddHandler mod_python .py
	PythonHandler mod_python.publisher
	PythonPath "sys.path+['/path/to/MyGlobals']"
	PythonImport MyGlobals /mydir


# Creates a subinterpreter "MyInterpreter" which handles the
# requests in this scope to be run there
PythonInterpreter MyInterpreter
PythonPath "sys.path+['/path/to/MyGlobals']"
PythonImport MyGlobals MyInterpreter

There are some caveats, however:

1) The imports happen at child initialization time, when a lot of the
configuration hasn't been merged in yet.  This includes:
PythonInterpreter (!!!), PythonOptions, ....

2) PythonImport is not really subinterpreter-scoped: it is a global
directive that specifies the interpreter name.  Plus PythonInterpreter
isn't in effect at the time of import, either.  It would be nice to
have a directive like

PythonInterpInit Foo

which would affect the interpreter "in the current scope" in the
apache configuration -- i.e. at the virtual server level by default,
or per directive / directory if those options are used.

3) This is not entirely specific to PythonImport, but it is difficult
in general to get your hands on configuration variables
(PythonOption-s, in particular) not in the context of a request.  It
would be nice if each subinterpreter had access to the Apache
configuration variables (e.g. PythonOptions) scope-local to it.

As a workaround, I'm using named interpreters and moving all
sub-interpreter-specific configuration into importable files.

4) Running with PythonAutoReload may still kill global variables if
you're not careful.


ps put this into the FAQ?

On Mon, 8 Mar 2004, Ben wrote:

> Hello,
> it seems like this is a question that is asked enough to be worth
> a) putting into the FAQ (for now), and
> b) eventually trying to solve.
> i used to do some apache API coding so i'd be willing to look into
> trying to support per-child (and possibly per-thread) initialization
> code.  i remember this used to be possible, and looking at mod_perl i
> see it has a PerlChildExitHandler.
> http://perl.apache.org/docs/2.0/user/handlers/server.html
> i'll start code-diving today, and let people know what i find.  (oh
> woe to the python programmer who has to read C!)
> take care, B
> ps i happen to want this for my project, which is an object / aspect
> oriented servlet framework, that supports mixin-style functionality
> for session-based authentication, caching, etc.  i plan on releasing
> that too, after some bugfixes and documentation.

More information about the Mod_python mailing list