[boost] Boost.Python

From: Dan Nuffer (dnuffer_at_[hidden])
Date: 2002-11-07 01:15:28

Hi,
I've started using Boost.Python to wrap some classes from OpenWBEM.  So 
far I've got one class mostly done: OW_String.  So far I have been very 
impressed, and think the library is great.  But I've had a few problems. 
  Here's some questions and comments:

1. It took me some searching to find 
BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS, I think it should be at least 
mentioned in the tutorial.

2. Is is possible to wrap member functions which take a variable number 
of arguments (e.g. int format(const char* fmt, ...); ) ?  I tried 
.def("format", &OW_String::format) but that doesn't work.

3. OW_String has some methods like OW_String& concat(const OW_String& 
arg); which return *this;.  I assume the correct return policy to use is 
return_internal_reference<>().  The documentation refers to the case 
where a reference is returned to an instance data member, but not the 
instance itself.  Is return_internal_reference correct in this case?

4. If the return policy is omitted from a member function which returns 
OW_String&, the error says: "specify_a_result_policy..."  This should 
say return, not result, since the documentation doesn't mention result 
policies.

5. It would be nice if you gave an example in the tutorial about how to 
specify overloads, since casting the member function pointer is not 
something that is completely obvious (at least it took me a while to 
figure it out).

6. How can I get python indexing and slicing to work on OW_String?  I 
couldn't see any information about this in the docs.

7. Do I need to expose the copy constructor and assignment operator via 
Boost.Python?

8. When I exposed the OW_String(const char*) and OW_String(char) 
constructors, python would always call OW_String(char) instead of 
OW_String(const char*).  Is this intentional or a bug?  I just removed 
the OW_String(char) constructor, since Python doesn't have chars anyway.

9. I have an operator<< defined, but .def(str(self)) doesn't compile. 
Here's the error: no matching function for call to `
    boost::python::class_<OW_String, boost::python::detail::not_specified,
    boost::python::detail::not_specified, 
boost::python::detail::not_specified>
    ::def(boost::python::str)'

10. I added implicitly_convertible<const char*,OW_String>(); It compiled 
fine, but it didn't work:
 >>> import owclient
 >>> s = owclient.OW_String("a")
 >>> s.concat(owclient.OW_String("b"))
<owclient.OW_String object at 0x817267c>
 >>> s.c_str()
'ab'
 >>> s.concat("c")
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: bad argument type for built-in operation

Any ideas why this didn't work?

Thanks!

--Dan Nuffer