[C++-sig] .def(str(self)) compile problems
Ralf W. Grosse-Kunstleve
rwgk at yahoo.com
Sun Feb 20 14:24:52 CET 2005
--- Simon Burton <simon at arrowtheory.com> wrote:
> I'm having trouble getting the __str__ wrapper for my C++ class to compile.
> Everything else i've tried works fine (methods/functions/operators), but when
> I include the .def( str(self) )
> line the compilation fails.
I am not sure, but I don't think Boost.Python supports what you want. I am not
even sure it could support automatic conversion from std::ostream to
std::string. However, I am sure you can get what you want in simple ways. For
- provide a function like this:
interval_as_str(interval const& self)
// conversion code here
- wrap like this:
Note that the unbound C++ interval_as_str() function is wrapped as a Python
Alternatively, if interval is your own class (as opposed to a class from a
third-party library) you could define a member function interval::as_str() and
wrap in the usual way:
There is yet another alternative that I often prefer. From a practical
viewpoint it is often the simplest alternative, but I've seen people having a
hard time getting their mind around it. I'll try to explain anyway.
First consider a pure Python example:
def __init__(self, (x,y)):
self.xy = (x,y)
p = point((1,2))
The output is:
<__main__.point instance at 0xb73f3f4c>
Now define this unbound function:
Almost what you want, but of course "print p" would be better than "print
point_as_str(p)". Here is the trick to make it work:
point.__str__ = point_as_str
If you come from a C++ background this Python feature may seem surprising.
However, as David Abrahams once told me, the whole secret is that "Python is a
To come back to your interval class: Simply remove the def(str(self) and inject
the __str__ method from Python:
return list(self.upper(self), self.lower(self))
lift.interval.__str__ = interval_as_str
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