Re: [boost] Boost::Python passing an instance as shared_ptr

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2001-12-11 23:36:46

John,

I'm afraid you're out-of-luck if you want it to work exactly that way. The
extension class doesn't hold its instances using a shared_ptr. Since the
instances are managed by other means, it would be a grave error to create a
shared_ptr to any of them. If you want to take a shared_ptr as an argument,
you must be sure that the original object was given to Python as a
shared_ptr. You could do that by exposing a factory function which produces
a shared_ptr<Name>.

-Dave

----- Original Message -----
From: "John Hunter" <jdhunter_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Tuesday, December 11, 2001 10:09 PM
Subject: [boost] Boost::Python passing an instance as shared_ptr

>
> I have two classes, Name and Person, which I have exposed to python.
> Person takes a shared_ptr<Name> in it's constructor.
>
> class Person {
> public:
>     Person( boost::shared_ptr<Name> pName, unsigned short age) ...
>     ...
> };
>
> I would like to be able to pass instances of 'Name' created in python
> to the Person constructor, i.e.,
>
> >>> from Person import Person, Name
> >>> n = Name("John", "D", "Hunter", "Ph.D")
> >>> p = Person( n, 33)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> RuntimeError: Object of extension class 'Name' does not wrap <4Name>.
>
> But this fails because n is an instance of Name, not a
> shared_ptr<Name>.  I suspect there is some to_python/from_python magic
> that would enable me to do this, but am not sure.  Is this possible?
> Does it even make sense to try?
>
> Thanks,
> John Hunter
>
> boost_1_26_0
>
> #include <string>
> #include <sstream>
> #include <iostream>
> #include <boost/smart_ptr.hpp>
> #include <boost/python/class_builder.hpp>
>
> class Name;
> typedef boost::shared_ptr<Name> PtrName;
>
> namespace python = boost::python;
>
> class Name {
> public:
>   Name( const std::string& first,
> const std::string& middle,
> const std::string& last,
> const std::string& letters = "") :
>     first(first), middle(middle), last(last), letters( letters)  {}
>
>
>   std::string get_first() const { return first;}
>   std::string get_last() const { return last;}
>   std::string get_middle() const { return middle;}
>   std::string get_letters() const { return letters;}
>   std::string get_full_name() const {
>     std::ostringstream os;
>     os << first << " "
>        << middle << " "
>        << last;
>     if (letters.size() > 0)
>       os << ", " << letters;
>     os << std::ends;
>     return os.str();
>   }
> private:
>   std::string first, middle, last, letters;
> };
>
> class Person;
> typedef boost::shared_ptr<Person> PtrPerson;
>
>
> class Person  {
> public:
>   Person(PtrName pName,
> unsigned short age) : pName(pName), age(age) {}
>   PtrName get_name() const { return pName;}
>   unsigned short get_age() const { return age;}
>   void happy_birthday() { ++age;}
>   void print() const

>     std::cout << pName->get_full_name()
>       << " is " << age << " years old." << std::endl;}
> private:
>   PtrName pName;
>   unsigned short age;
> };
>
>
> class NamePy : public python::class_builder<Name>
>

> public:
>   NamePy(python::module_builder&, const std::string& className);
> };
>
>
>
>
> NamePy::NamePy(python::module_builder& m, const std::string& className)
>   : python::class_builder<Name>(m, className.c_str())
> {
>
def(python::constructor<std::string,std::string,std::string,std::string>());
>   def(&Name::get_first, "get_first");
>   def(&Name::get_middle, "get_middle");
>   def(&Name::get_last, "get_last");
>   def(&Name::get_letters, "get_letters");
> }
>
> class PersonPy : public python::class_builder<Person>
>

> public:
>   PersonPy(python::module_builder&, const std::string& className);
> };
>
>
> PersonPy::PersonPy(python::module_builder& m, const std::string&
className)
>   : python::class_builder<Person>(m, className.c_str())
> {
>   def(python::constructor<PtrName, unsigned short>());
>   def(&Person::get_name, "get_name");
>   def(&Person::get_age, "get_age");
>   def(&Person::happy_birthday, "happy_birthday");
>   def(&Person::print, "whois");
> }
>
> BOOST_PYTHON_MODULE_INIT(Person)
> {
>
>   boost::python::module_builder m( "Person" );
>
>   PersonPy person( m, "Person" );
>   NamePy name( m, "Name" );
>
> }
>
>
>
>
>
>
>
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