Hi all,
I'm inches away from getting an extension working that allows Python scripts
to be used as components in SCA C++. I should be putting that up some time
tomorrow - I'll start a thread about a few minor issues with the extension
framework that I've come across, but it hasn't been too complex to get this
going.
At the moment the extension provides an implementation.python element to the
.composite of the form:
<implementation.python module="PythonModuleName"
path="relative/path/to/module" class="PythonClassName"/>
This allows other C++ components or C++ clients to call the service
implemented by code inside the Python module. The service interface is
currently described by a C++ header file, and uses the
interface.cppinterface binding. Currently, references from the Python
components are not
enabled (see below).
There are two further areas that are needed for full integration of Python
into SCA (or SCA into Python):
1) A programming model for SCA in Python to allow Python components or
Python clients to call SCA services. This will enable components with Python
implementations to have references.
We could either create a Python extension that will emulate the service
lookup that we do in C++, e.g. a Python equivalent of the following C++
snippet:
// First, get the current ComponentContext
osoa::sca::ComponentContext myContext =
osoa::sca::ComponentContext::getCurrent();
// Find the required service, as referenced in
CalculatorImpl.componentType
DivideService* divideService =
(DivideService*)myContext.getService("divideService");
// Finally, invoke the service
result = divideService->divide(arg1, arg2);
Alternatively, we could look at doing some kind of annotations within the
Python component module - I'm not sure whether Python has annotation support
(I don't believe so), or whether there is a way to 'fake' it to make
comments/documentation act as annotations.
2) An interface.python extension so that python components do not have to
have their interfaces converted to a C++ or WSDL description. Due to the
loose typing that Python allows this isn't the easiest thing to do - most
functions have signatures like: def myMethod(arg1, arg2) - and (as far as I
can currently tell) there is no way to determine the types of the arguments
or return values aside from at invocation time.
At the moment the SCAGEN tool generates the C++ component proxy and wrapper
classes based on the C++ header specified in the interface.cpp element in
the .componentType file. If the .componentType file has an
interface.pythonelement instead, and specifies the Python module,
generating the correct C++
code neccessary to call the python service is hard. Alternatively, the
interface.python could specify the function signatures itself, but that
starts to stray into WSDL territory, e.g:
<interface.python>
<function name="myMethod">
<argument name="arg1" type="string"/>
<argument name="arg2" type="int"/>
<return type="string"/>
</function>
</interface.python>
There may well be a way to specify things a bit tighter in Python that i
don't know about - I'll keep looking into this.
What do people think about these various issues? Has anyone got any
suggestions?
Thanks!
Andy
