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From: <rom...@us...> - 2007-04-15 19:24:57
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Revision: 990
http://svn.sourceforge.net/pygccxml/?rev=990&view=rev
Author: roman_yakovenko
Date: 2007-04-15 12:24:57 -0700 (Sun, 15 Apr 2007)
Log Message:
-----------
adding "exceptions" lesson
Modified Paths:
--------------
pyplusplus_dev/docs/troubleshooting_guide/exceptions/exceptions.rest
Added Paths:
-----------
pyplusplus_dev/docs/troubleshooting_guide/exceptions/exceptions.zip
Modified: pyplusplus_dev/docs/troubleshooting_guide/exceptions/exceptions.rest
===================================================================
--- pyplusplus_dev/docs/troubleshooting_guide/exceptions/exceptions.rest 2007-04-15 18:57:23 UTC (rev 989)
+++ pyplusplus_dev/docs/troubleshooting_guide/exceptions/exceptions.rest 2007-04-15 19:24:57 UTC (rev 990)
@@ -10,42 +10,52 @@
.. include:: ./definition.rest
--------
-Content
--------
+-------------------
+What's the problem?
+-------------------
-This example actually consist from 2 small, well documented examples.
+It is all about module interface and user expectations. If you can translate all
+your exceptions to built-in ones, than you are fine. You don't have to read this
+"lesson", but Boost.Python `exception translator`_ documentation.
-The first one shows how to handle conversion between tuples: `boost::tuples::tuple`_
-and Python tuple.
+.. _`exception translator` : http://boost.org/libs/python/doc/v2/exception_translator.html
-.. _`boost::tuples::tuple` : http://boost.org/libs/tuple/doc/tuple_users_guide.html
+My use case was different. I was supposed to export the exception classes and make
+them play nice with the ``try ... except`` mechanism. I mean, users should be able
+to:
-The second one shows how to add an automatic conversion from Python tuple to
-some registered class. The class registration allows you to use its functionality
-and enjoy from automatic conversion.
+ 1. "except" all exceptions using ``except Exception, err:`` statement
+ 2. "except" the exposed library defined exception classes
+
+I thought about few possible solutions to the problem. My first attempt was to
+add a missing functionality to Boost.Python library. Well, I quickly found out
+that the task is not a trivial one.
+
+The next solution, I thought about, was to expose the exception class as-is and
+to define new class in Python, which derives from it and the built-in ``Exception``.
+I implemented it and when I run the code I've got ``TypeError``:
+"Error when calling the metaclass bases multiple bases have instance lay-out conflict".
+
+The only solution left was to use "aggregation with automatic delegation". I mean
+instead of deriving from the exception class, I will keep it as a member variable
+in a class defined in Python, which derives from the built-in ``Exception`` one.
+Every time user access an attribute, the class defined in Python will automatically
+redirect the request to the variable. This technique is explained much better here:
+http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52295 .
+
Files
-----
-* `tuples.hpp`_ file contains Boost.Tuple to\\from Python tuple conversion
- implementation
+* `exceptions.cpp`_ file contains source code for the "lesson"
-* `tuples_tester.cpp`_ file contains few functions, which test the tuples
- conversion functionality
-
-* `custom_rvalue.cpp`_ file contains example of registration custom r-value
- converter
-
* `sconstruct`_ file contains build instructions for scons build tool.
-* `test.py`_ file contains complete unit tests for both example
+* `test.py`_ file contains complete unit test suite
All files contain comments, which describe what and why was done.
-.. _`tuples.hpp` : ./tuples.hpp.html
-.. _`tuples_tester.cpp` : ./tuples_tester.cpp.html
-.. _`custom_rvalue.cpp` : ./custom_rvalue.cpp.html
+.. _`exceptions.cpp` : ./exceptions.cpp.html
.. _`sconstruct` : ./sconstruct.html
.. _`test.py` : ./test.py.html
@@ -53,9 +63,9 @@
Download
--------
-`automatic_conversion.zip`_
+`exceptions.zip`_
-.. _`automatic_conversion.zip` : ./automatic_conversion.zip
+.. _`exceptions.zip` : ./exceptions.zip
.. _`Py++` : ./../pyplusplus.html
Added: pyplusplus_dev/docs/troubleshooting_guide/exceptions/exceptions.zip
===================================================================
(Binary files differ)
Property changes on: pyplusplus_dev/docs/troubleshooting_guide/exceptions/exceptions.zip
___________________________________________________________________
Name: svn:mime-type
+ application/octet-stream
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