...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Ralf W. Grosse-Kunstleve provides these notes:
Using the regular class_<>
wrapper:
class_<std::vector<double> >("std_vector_double") .def(...) ... ;
This can be moved to a template so that several types (double
, int
,
long
, etc.) can be wrapped
with the same code. This technique is used in the file scitbx/include/scitbx/array_family/boost_python/flex_wrapper.h
in the "scitbx" package.
The file could easily be modified for wrapping std::vector<>
instantiations. This type of
C++/Python binding is most suitable for containers that may contain a
large number of elements (>10000).
Using custom rvalue converters. Boost.Python "rvalue converters" match function signatures such as:
void foo(std::vector<double> const &array); // pass by const-reference void foo(std::vector<double> array); // pass by value
Some custom rvalue converters are implemented in the file scitbx/include/scitbx/boost_python/container_conversions.h
This code can be used to convert
from C++ container types such as std::vector<>
or std::list<>
to Python tuples and vice versa.
A few simple examples can be found in the file scitbx/array_family/boost_python/regression_test_module.cpp
Automatic C++ container <-> Python tuple conversions are most suitable
for containers of moderate size. These converters generate significantly
less object code compared to alternative 1 above.
A disadvantage of using alternative 2 is that operators such as arithmetic +,-,*,/,% are not available. It would be useful to have custom rvalue converters that convert to a "math_array" type instead of tuples. This is currently not implemented but is possible within the framework of Boost.Python V2 as it will be released in the next couple of weeks. [ed.: this was posted on 2002/03/10]
It would also be useful to also have "custom lvalue converters"
such as std::vector<>
<-> Python list. These converters would support the modification of
the Python list from C++. For example:
C++:
void foo(std::vector<double> &array) { for(std::size_t i=0;i<array.size();i++) { array[i] *= 2; } }
Python:
>>> l = [1, 2, 3] >>> foo(l) >>> print l [2, 4, 6]
Custom lvalue converters require changes to the Boost.Python core library and are currently not available.
P.S.:
The "scitbx" files referenced above are available via anonymous CVS:
cvs -d:pserver:anonymous@cvs.cctbx.sourceforge.net:/cvsroot/cctbx login cvs -d:pserver:anonymous@cvs.cctbx.sourceforge.net:/cvsroot/cctbx co scitbx