| 1 | <!-- Copyright David Abrahams 2006. Distributed under the Boost --> |
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| 4 | <html> |
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| 5 | <head> |
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| 7 | <link rel="stylesheet" type="text/css" href="../boost.css"> |
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| 8 | <title>Boost.Python - April 2002 Progress Report</title> |
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| 9 | </head> |
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| 10 | <body link="#0000ff" vlink="#800080"> |
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| 11 | <table border="0" cellpadding="7" cellspacing="0" width="100%" summary= |
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| 12 | "header"> |
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| 13 | <tr> |
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| 14 | <td valign="top" width="300"> |
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| 15 | <h3><a href="../../../../index.htm"><img height="86" width="277" alt= |
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| 16 | "C++ Boost" src="../../../../boost.png" border="0"></a></h3> |
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| 17 | </td> |
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| 18 | <td valign="top"> |
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| 19 | <h1 align="center"><a href="../index.html">Boost.Python</a></h1> |
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| 20 | <h2 align="center">April 2002 Progress Report</h2> |
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| 21 | </td> |
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| 22 | </tr> |
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| 23 | </table> |
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| 24 | <hr> |
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| 25 | <h2>Contents</h2> |
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| 26 | <dl class="index"> |
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| 27 | <dt><a href="#accomplishments">Accomplishments</a></dt> |
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| 28 | <dl class="index"> |
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| 29 | <dt><a href="#arity">Arbitrary Arity Support</a></dt> |
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| 30 | <dt><a href="#callbacks">New Callback Interface</a></dt> |
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| 31 | <dt><a href="#policies">Call Policies for Construtors</a></dt> |
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| 32 | <dt><a href="#bugs">Real Users, Real Bugs</a></dt> |
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| 33 | <dt><a href="#insights">New Insights</a></dt> |
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| 34 | <dt><a href="#v1">Boost.Python V1 Maintenance</a></dt> |
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| 35 | </dl> |
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| 36 | |
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| 37 | <dt><a href="#missing">What's Missing</a></dt> |
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| 38 | |
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| 39 | </dl> |
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| 40 | |
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| 41 | <h2><a name="accomplishments">Accomplishments</a></h2> |
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| 42 | |
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| 43 | April was a short month as far as Boost.Python was concerned, since |
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| 44 | the spring ISO C++ Committee Meeting (and associated vacation) |
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| 45 | occupied me for the 2nd half of the month. However, a suprising amount |
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| 46 | of work got done... |
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| 47 | |
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| 48 | <h3><a name="arity">Arbitrary Arity Support</a></h3> |
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| 49 | |
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| 50 | I began using the <a |
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| 51 | href="../../../preprocessor/doc/index.html">Boost.Preprocessor</a> |
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| 52 | metaprogramming library to generate support for functions and member |
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| 53 | functions of arbitrary arity, which was, to say the least, quite an |
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| 54 | adventure. The feedback cycle resulting from my foray into |
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| 55 | Boost.Preprocessor resulted in several improvements to the library, |
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| 56 | most notably in its documentation. |
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| 57 | |
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| 58 | <p> |
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| 59 | |
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| 60 | Boost.Python now supports calls of up to 17 arguments on most |
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| 61 | compilers. Because most EDG-based compilers have dismal preprocessor |
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| 62 | performance, I had to "manually" expand the metaprograms for |
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| 63 | arities from zero to fifteen arguments, and EDG-based compilers with |
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| 64 | <code>__EDG_VERSION__ <= 245</code> only support 15 |
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| 65 | arguments by default. If some crazy program finds a need for more than |
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| 66 | the default arity support, users can increase the base support by |
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| 67 | setting the <code>BOOST_PYTHON_MAX_ARITY</code> preprocessor symbol. |
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| 68 | |
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| 69 | <h3><a name="callbacks">New Callback Interface</a></h3> |
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| 70 | |
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| 71 | I mentioned in <a href="Mar2002.html">last month's report</a> that I |
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| 72 | wasn't pleased with the interface for the interface for calling into |
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| 73 | Python, so now it has been redesigned. The new interface is outlined |
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| 74 | in <a |
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| 75 | href="http://mail.python.org/pipermail/c++-sig/2002-April/000953.html">this |
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| 76 | message</a> (though the GCC 2.95.3 bugs have been fixed). |
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| 77 | |
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| 78 | <h3><a name="policies">Call Policies for Constructors</a></h3> |
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| 79 | |
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| 80 | On April 2nd, I <a |
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| 81 | href="http://mail.python.org/pipermail/c++-sig/2002-April/000916.html">announced</a> |
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| 82 | support for the use of call policies with constructors. |
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| 83 | |
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| 84 | <h3><a name="bugs">Real Users, Real Bugs</a></h3> |
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| 85 | |
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| 86 | At least two people outside of Kull began actually using Boost.Python |
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| 87 | v2 in earnest this month. Peter Bienstman and Pearu Pearson both |
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| 88 | provided valuable real-world bug reports that helped me to improve the |
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| 89 | library's robustness. |
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| 90 | |
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| 91 | <h3><a name="insights">New Insights</a></h3> |
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| 92 | |
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| 93 | <a |
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| 94 | href="http://mail.python.org/pipermail/c++-sig/2002-May/001010.html" |
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| 95 | >Answering some of Pearu's questions</a> about explicitly converting |
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| 96 | objects between Python and C++ actually led me to a new understanding |
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| 97 | of the role of the current conversion facilities. In Boost.Python v1, |
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| 98 | all conversions between Python and C++ were handled by a single family |
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| 99 | of functions, called <code>to_python()</code> and |
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| 100 | <code>from_python()</code>. Since the primary role of Boost.Python is |
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| 101 | to wrap C++ functions in Python, I used these names for the first kind |
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| 102 | of converters I needed: those that extract C++ objects to be used as |
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| 103 | function arguments and which C++ function return values to |
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| 104 | Python. The better-considered approach in Boost.Python v2 uses a |
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| 105 | completely different mechanism for conversions used when calling |
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| 106 | Python from C++, as in wrapped virtual function implementations. I |
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| 107 | usually think of this as a "callback", as in "calling |
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| 108 | back into Python", and I named the converters used in callbacks |
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| 109 | accordingly: <code>to_python_callback</code> and |
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| 110 | <code>from_python_callback</code>. However, as it turns out, the |
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| 111 | behavior of the "callback" converters is the appropriate one |
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| 112 | for users who want to explicitly extract a C++ value from a Python |
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| 113 | object, or create a Python object from a C++ value. The upshot is that |
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| 114 | it probably makes sense to change the name of the existing <code>to_python</code> and |
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| 115 | <code>from_python</code> so those names are available for the |
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| 116 | user-friendly explicit converters. |
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| 117 | |
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| 118 | <p> |
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| 119 | <a |
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| 120 | href="http://mail.python.org/pipermail/c++-sig/2002-May/001013.html">Another |
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| 121 | of Pearu's questions</a> pushes momentum further in the direction of a |
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| 122 | more-sophisticated overloading mechanism than the current |
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| 123 | simple-minded "first match" approach, as I suggested <a |
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| 124 | href="Mar2002.html#implicit_conversions">last month</a>. |
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| 125 | |
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| 126 | <h3><a name="v1">Boost.Python V1 Maintenance</a></h3> |
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| 127 | |
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| 128 | As much as I'm looking forward to retiring Boost.Python v1, a |
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| 129 | significant amount of effort has been being spent dealing with support |
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| 130 | problems; the saying that code rots when left alone is true, and |
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| 131 | Boost.Python is no exception. Eventually it became obvious to me that |
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| 132 | we were going to have to invest some effort in keeping V1 healthy |
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| 133 | while working on V2. Ralf and I have expanded support for various |
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| 134 | compilers and stabilized the V1 codebase considerably. We discarded |
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| 135 | the obsolete Visual Studio projects which were causing so much |
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| 136 | confusion. Still to do before the next Boost release: |
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| 137 | <ol> |
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| 138 | <li>Update the build/test documentation with detailed instructions for |
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| 139 | configuring various toolsets. |
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| 140 | <li>Provide some links to Boost.Python v2 to let people know what's |
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| 141 | coming. |
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| 142 | </ol> |
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| 143 | |
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| 144 | |
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| 145 | <h2><a name="missing">What's Missing</a></h2> |
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| 146 | |
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| 147 | Last month I announced that I would implement the following which are |
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| 148 | not yet complete: |
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| 149 | <ol> |
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| 150 | <li>Document all implemented features |
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| 151 | <li>Implement conversions for <code>char</code> types. This is |
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| 152 | implemented but not tested, so we have to assume it doesn't work. |
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| 153 | </ol> |
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| 154 | |
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| 155 | These are my first priority for this month (especially the |
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| 156 | documentation). |
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| 157 | |
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| 158 | <p>Revised |
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| 159 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
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| 160 | 13 November, 2002 |
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| 161 | <!--webbot bot="Timestamp" endspan i-checksum="39359" --> |
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| 162 | </p> |
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| 163 | <p><i>© Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a> |
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| 164 | 2002. </i></p> |
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| 165 | </body> |
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| 166 | </html> |
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