[C++-sig] __str__ method for wrapper classes

[Alex Mohr]

> I want to be able to print MyClass as a string in python. I 
> added .def(str(self)) to the class object for the wrapper (MyClassWrap) 
> thinking it would work but, python complains that the __str__ method did not 
> match the C++ signature:
> 
> Boost.Python.ArgumentError: Python argument types in
>     MyClass.__str__(MyClass)
> did not match C++ signature:
>     __str__(MyClassWrap {lvalue})
> 
> I think the problem is that I defined the __str__ method for MyClassWrap and 
> not for MyClass. Since MyClassWrap also inherits from wrapper, it can't use 
> MyClass's extraction operator. I don't have a class_ object for MyClass. I 
> only have it for MyClassWrap and the other classes that inherit from MyClass. 
> How do I fix this?

 From a cursory inspection, I believe this is the same bug as that 
mentioned in this thread:

http://mail.python.org/pipermail/c++-sig/2006-September/011336.html

which David has already fixed in CVS.  Unfortunately, I don't know when 
the next version of boost (and boost python) will be out, so I can't say 
when you'll get it.

As a workaround, I think you can do something like this in your wrapping 
code:

class<...>(...)
     .def("__str__", boost::lexical_cast<std::string, MyClass const &>)

if MyClass is streamable.  If it's not, you can always do something 
totally custom:

static std::string MyClass__str__(MyClass const &self) {
     return std::string("Whatever I want.");
}

class<...>(...)
     .def("__str__", MyClass__str__)

Alex