PyEval_GetLocals and unreferenced variables

[Kasper Peeters]

> >     def fun():
> >        cfun_that_creates_q_in_local_scope()
> >        def fun2():
> >            cfun_that_wants_to_see_if_q_is_available()
> > 
> > So the Python side actually doesn't see 'q' directly at all.
>
> I think you will need to elaborate.

Ok, here goes (and thanks for listening). 

The behaviour of the C side is determined by certain
settings/preferences. I want these settings to respect the Python
scope. I could in principle decide to make these settings a proper
Python object, and ask the user to create one and pass it along at
every C-function call. Something like

   def fun():
      settings = Cpp_Options()
      settings.set_some_flag()
      cfun(settings, ...)
      def fun2():
          settings = Cpp_Options(settings)
          settings.set_some_other_flag()
          cfun(settings, ...)

Then Python would automatically take care of the scope of 'settings'.

However, this is difficult for the user to keep track of. So my
idea was to allow for

  def fun():
      set_some_flag()
      cfun(...)
      def fun2():
          set_some_other_flag()
          cfun(...)

I let the C side create a Cpp_Options object on the locals stack
behind the scenes, and the 'cfun()' function takes it from there
directly, without requiring the user to pass it. Much easier for the
user.

This works, but the problem is that the C side does not see the
settings that were created in fun() when it gets called from fun2(). In
fun2(), the locals do not contain objects constructed earlier in fun(),
unless the Python side explicitly refers to them. So adding a line

    settings.do_something()

inside fun2() would work and forces Python to pull the settings object
created in fun() into scope, but that sort of defeats the purpose.

Hence my question: how can I ask, purely on the C side, for Python to
pull objects into the local frame?

Final note: I am actually trying to make this look as close as possible
to an older custom-built language, which didn't require passing the
settings object either, so it's kinda important to make the user feel
'at home'. 

Hope this makes it more clear, thanks for your patience.

Cheers,
Kasper