Re: [boost] Re: newbie: python and reference

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2001-09-13 09:41:59

Thomas,

Thank you for your interest in contributing to Boost.Python!

I think I was supposed to reply to your previous email, and got distracted
by one of my many responsibilities. I assume you are referring to
http://groups.yahoo.com/group/boost/message/17093. I will try to respond
today.

Regarding your "ref" proposal, there is quite a bit of detail missing, but I
have the following reservations:

1. "ref" is a term used in Boost.Python to refer to a generic Python Object
reference. It is a typedef for boost::python::reference<PyObject>. I think
your use of the term could be confusing.

2. Currently, it is possible to wrap a function taking int const&
parameters: it just works automatically. The reason that no facility for
wrapping int& parameters is provided is that Python ints are immutable. We
don't want people changing them: it would break everything.

3. More importantly, AFAICT it opens a dangerous hole which would allow
users to easily crash Python. If you are holding on to a pointer to some
object which is contained in another Python object, what happens to the
pointer when the Python object it points to is destroyed/garbage collected?
I say "AFAICT" above because I can't see the details of your code, so you
may be doing something utterly different than what I expect.

-Dave

----- Original Message -----
From: "Thomas Malik" <Thomas_Malik%LGBANK_at_[hidden]>

to_python/from_python/make_ref
template functions.
Use is as follows:
in refmodule.cpp:
BOOST_PYTHON_MODULE_INIT(ref)
{
  try
  {
      python::module_builder this_module("ref");
      this_module.def(make_ref<int>, "make_ref");
      this_module.def(make_ref<const char*>, "make_ref");
     ... other reference types needed
  }
  catch(...)
  {
      python::handle_exception();
  }
}

reftest.py
import ref
>> r=ref.make_ref(1)
>> print r
<reference to int object at b4f40>
>> print type(r)
<type 'reference to int'>
>> print r()
1
>> function_with_intref_parameter(r)
>> print r()
10

The whole module is fairly short. Any interest ?

BTW. did my first mail, concerning unsigned char* conversions did get to
the mailing list ?
I didn't receive any comments on it.

--
Thomas Malik
Landesbank Baden-Wuerttemberg (Stuttgart, Germany)
Abt. 2340 Tel. [phone]
Thomas_Malik%lgbank_at_[hidden]
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