8.1 Extending PyS60
The general rules and guidelines for writing Python extensions apply
in the S60 Python environment as well.
The steps for the implementation of an extension modules include:
- Preparation of the data structures that make the C/C++ coded extensions
visible to the Python interpreter and make it possible to perform calls from
Python to C/C++ code
- Conversions between C/C++ representations of the Python objects and
object types used in the extension code
- Maintenance of the reference counts of the C/C++ representations of the
- Passing of exceptions between C/C++ code and Python
- Management of interpreter's thread state and the interpreter lock
In addition to the concerns common for all Python C extensions, the
following principles should be considered when implementing new Python
interfaces in the S60 environment:
- Maximize the usage of Python's built-in types at the interfaces.
- Related to the above: design interfaces in such a way that information
can be passed between them with minimal conversions.
- Convert Symbian operating system exceptions or errors to Python exceptions.
- Unicode strings are used at the interfaces to represent text that gets
shown on the GUI. They can be passed to and from Symbian operating system
- While performing potentially long-lasting or blocking calls from an
extension implementation to services outside the interpreter, the
interpreter lock must be released and then re-acquired after the call.
- Rather than always implementing a thin wrapper on top of a Symbian OS
facility, consider the actual task for which the script writer needs the
particular interface. For example, if the task involves interaction with
the users using the GUI, the script writer's interest may well be limited
to performing the interaction or information exchange in a way that is
compatible with the UI style rather than having full control of the
low-level details of the GUI implementation.
- The C/C++ implementation of a Python interface should be optimized for
performance and covering access to the necessary features of the
underlying Platform. Where necessary, the Python programming interface can
be further refined by wrapper modules written in Python.
The pyd name should be of the format 'kf_<module-name>.pyd'. Note that this change
is required only for the pyd name and module name is not required to have this prefix.
The module initialization function must be exported at ordinal 1. The module
identification is based on the filename only. As a special feature of PyS60, an
optional module finalizer function may be exported at ordinal 2.
The extension modules added by the developer should be placed in the module repo
folder of the PyS60 Application Packager so that the compiled PYD's can be picked
up while packaging. For information on this topic refer 8.1.3, Distributing Extension Modules.
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