| Daniel Veillard | 6dbcaf8 | 2002-02-20 14:37:47 +0000 | [diff] [blame^] | 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd"> |
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| 13 | <title>Python and bindings</title> |
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| 18 | <a href="http://www.gnome.org/"><img src="smallfootonly.gif" alt="Gnome Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo"></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo"></a> |
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| 20 | <td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"> |
| 21 | <h1>The XML C library for Gnome</h1> |
| 22 | <h2>Python and bindings</h2> |
| 23 | </td></tr></table></td></tr></table></td> |
| 24 | </tr></table> |
| 25 | <table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr> |
| 26 | <td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td> |
| 27 | <table width="100%" border="0" cellspacing="1" cellpadding="3"> |
| 28 | <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr> |
| 29 | <tr><td bgcolor="#fffacd"><ul> |
| 30 | <li><a href="index.html">Home</a></li> |
| 31 | <li><a href="intro.html">Introduction</a></li> |
| 32 | <li><a href="FAQ.html">FAQ</a></li> |
| 33 | <li><a href="docs.html">Documentation</a></li> |
| 34 | <li><a href="bugs.html">Reporting bugs and getting help</a></li> |
| 35 | <li><a href="help.html">How to help</a></li> |
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| 37 | <li><a href="news.html">News</a></li> |
| 38 | <li><a href="XMLinfo.html">XML</a></li> |
| 39 | <li><a href="XSLT.html">XSLT</a></li> |
| 40 | <li><a href="python.html">Python and bindings</a></li> |
| 41 | <li><a href="architecture.html">libxml architecture</a></li> |
| 42 | <li><a href="tree.html">The tree output</a></li> |
| 43 | <li><a href="interface.html">The SAX interface</a></li> |
| 44 | <li><a href="xmldtd.html">Validation & DTDs</a></li> |
| 45 | <li><a href="xmlmem.html">Memory Management</a></li> |
| 46 | <li><a href="encoding.html">Encodings support</a></li> |
| 47 | <li><a href="xmlio.html">I/O Interfaces</a></li> |
| 48 | <li><a href="catalog.html">Catalog support</a></li> |
| 49 | <li><a href="library.html">The parser interfaces</a></li> |
| 50 | <li><a href="entities.html">Entities or no entities</a></li> |
| 51 | <li><a href="namespaces.html">Namespaces</a></li> |
| 52 | <li><a href="upgrade.html">Upgrading 1.x code</a></li> |
| 53 | <li><a href="threads.html">Thread safety</a></li> |
| 54 | <li><a href="DOM.html">DOM Principles</a></li> |
| 55 | <li><a href="example.html">A real example</a></li> |
| 56 | <li><a href="contribs.html">Contributions</a></li> |
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| 58 | <a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a> |
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| 61 | </table> |
| 62 | <table width="100%" border="0" cellspacing="1" cellpadding="3"> |
| 63 | <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr> |
| 64 | <tr><td bgcolor="#fffacd"><ul> |
| 65 | <li><a href="APIchunk0.html">Alphabetic</a></li> |
| 66 | <li><a href="APIconstructors.html">Constructors</a></li> |
| 67 | <li><a href="APIfunctions.html">Functions/Types</a></li> |
| 68 | <li><a href="APIfiles.html">Modules</a></li> |
| 69 | <li><a href="APIsymbols.html">Symbols</a></li> |
| 70 | </ul></td></tr> |
| 71 | </table> |
| 72 | <table width="100%" border="0" cellspacing="1" cellpadding="3"> |
| 73 | <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr> |
| 74 | <tr><td bgcolor="#fffacd"><ul> |
| 75 | <li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li> |
| 76 | <li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li> |
| 77 | <li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li> |
| 78 | <li><a href="ftp://xmlsoft.org/">FTP</a></li> |
| 79 | <li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li> |
| 80 | <li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li> |
| 81 | <li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Bug Tracker</a></li> |
| 82 | </ul></td></tr> |
| 83 | </table> |
| 84 | </td></tr></table></td> |
| 85 | <td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"> |
| 86 | <p>There is a number of language bindings and wrappers available for libxml2, |
| 87 | the list below is not exhaustive. Please contact the <a href="http://mail.gnome.org/mailman/listinfo/xml-bindings">xml-bindings@gnome.org</a> |
| 88 | (<a href="http://mail.gnome.org/archives/xml-bindings/">archives</a>) in |
| 89 | order to get updates to this list or to discuss the specific topic of libxml2 |
| 90 | or libxslt wrappers or bindings:</p> |
| 91 | <ul> |
| 92 | <li> |
| 93 | <a href="mailto:ari@lusis.org">Ari Johnson</a> |
| 94 | provides a C++ wrapper for libxml:<br> |
| 95 | Website: <a href="http://lusis.org/~ari/xml++/">http://lusis.org/~ari/xml++/</a><br> |
| 96 | Download: <a href="http://lusis.org/~ari/xml++/libxml++.tar.gz">http://lusis.org/~ari/xml++/libxml++.tar.gz</a> |
| 97 | </li> |
| 98 | <li>There is another <a href="http://libgdome-cpp.berlios.de/">C++ wrapper |
| 99 | based on the gdome2 </a>bindings maintained by Tobias Peters.</li> |
| 100 | <li> |
| 101 | <a href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt |
| 102 | Sergeant</a> |
| 103 | developped <a href="http://axkit.org/download/">XML::LibXSLT</a>, a perl |
| 104 | wrapper for libxml2/libxslt as part of the <a href="http://axkit.com/">AxKit XML application server</a> |
| 105 | </li> |
| 106 | <li> |
| 107 | <a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> |
| 108 | provides and earlier version of the libxml/libxslt <a href="http://www.rexx.com/~dkuhlman">wrappers for Python</a> |
| 109 | </li> |
| 110 | <li>Petr Kozelka provides <a href="http://sourceforge.net/projects/libxml2-pas">Pascal units to glue |
| 111 | libxml2</a> with Kylix, Delphi and other Pascal compilers</li> |
| 112 | <li>Wai-Sun "Squidster" Chia provides <a href="http://www.rubycolor.org/arc/redist/">bindings for Ruby</a> and |
| 113 | libxml2 bindings are also available in Ruby through the <a href="http://libgdome-ruby.berlios.de/">libgdome-ruby</a> module |
| 114 | maintained by Tobias Peters.</li> |
| 115 | </ul> |
| 116 | <p>The distribution includes a set of Python bindings, which are garanteed to |
| 117 | be maintained as part of the library in the future, though the Python |
| 118 | interface have not yet reached the maturity of the C API. The distribution |
| 119 | includes a set of examples and regression tests for the python bindings in |
| 120 | the <code>python/tests</code> directory. Here are some excepts from those |
| 121 | tests:</p> |
| 122 | <h3>tst.py:</h3> |
| 123 | <p>This is a basic test of the file interface and DOM navigation:</p> |
| 124 | <pre>import libxml2 |
| 125 | |
| 126 | doc = libxml2.parseFile("tst.xml") |
| 127 | if doc.name != "tst.xml": |
| 128 | print "doc.name failed" |
| 129 | sys.exit(1) |
| 130 | root = doc.children |
| 131 | if root.name != "doc": |
| 132 | print "root.name failed" |
| 133 | sys.exit(1) |
| 134 | child = root.children |
| 135 | if child.name != "foo": |
| 136 | print "child.name failed" |
| 137 | sys.exit(1) |
| 138 | doc.freeDoc()</pre> |
| 139 | <p>The Python module is called libxml2, parseFile is the equivalent of |
| 140 | xmlParseFile (most of the bindings are automatically generated, and the xml |
| 141 | prefix is removed and the casing convention are kept). All node seen at the |
| 142 | binding level share the same subset of accesors:</p> |
| 143 | <ul> |
| 144 | <li> |
| 145 | <code>name</code> |
| 146 | : returns the node name</li> |
| 147 | <li> |
| 148 | <code>type</code> |
| 149 | : returns a string indicating the node typ<code>e</code> |
| 150 | </li> |
| 151 | <li> |
| 152 | <code>content</code> |
| 153 | : returns the content of the node, it is based on xmlNodeGetContent() and |
| 154 | hence is recursive.</li> |
| 155 | <li> |
| 156 | <code>parent</code> |
| 157 | , <code>children</code>, <code>last</code>, <code>next</code>, |
| 158 | <code>prev</code>, <code>doc</code>, <code>properties</code>: pointing to |
| 159 | the associated element in the tree, those may return None in case no such |
| 160 | link exists.</li> |
| 161 | </ul> |
| 162 | <p>Also note the need to explicitely deallocate documents with freeDoc() . |
| 163 | Reference counting for libxml2 trees would need quite a lot of work to |
| 164 | function properly, and rather than risk memory leaks if not implemented |
| 165 | correctly it sounds safer to have an explicit function to free a tree. The |
| 166 | wrapper python objects like doc, root or child are them automatically garbage |
| 167 | collected.</p> |
| 168 | <h3>validate.py:</h3> |
| 169 | <p>This test check the validation interfaces and redirection of error |
| 170 | messages:</p> |
| 171 | <pre>import libxml2 |
| 172 | |
| 173 | #desactivate error messages from the validation |
| 174 | def noerr(ctx, str): |
| 175 | pass |
| 176 | |
| 177 | libxml2.registerErrorHandler(noerr, None) |
| 178 | |
| 179 | ctxt = libxml2.createFileParserCtxt("invalid.xml") |
| 180 | ctxt.validate(1) |
| 181 | ctxt.parseDocument() |
| 182 | doc = ctxt.doc() |
| 183 | valid = ctxt.isValid() |
| 184 | doc.freeDoc() |
| 185 | if valid != 0: |
| 186 | print "validity chec failed"</pre> |
| 187 | <p>The first thing to notice is the call to registerErrorHandler(), it |
| 188 | defines a new error handler global to the library. It is used to avoid seeing |
| 189 | the error messages when trying to validate the invalid document.</p> |
| 190 | <p>The main interest of that test is the creation of a parser context with |
| 191 | createFileParserCtxt() and how the behaviour can be changed before calling |
| 192 | parseDocument() . Similary the informations resulting from the parsing phase |
| 193 | are also available using context methods.</p> |
| 194 | <p>Contexts like nodes are defined as class and the libxml2 wrappers maps the |
| 195 | C function interfaces in terms of objects method as much as possible. The |
| 196 | best to get a complete view of what methods are supported is to look at the |
| 197 | libxml2.py module containing all the wrappers.</p> |
| 198 | <h3>push.py:</h3> |
| 199 | <p>This test show how to activate the push parser interface:</p> |
| 200 | <pre>import libxml2 |
| 201 | |
| 202 | ctxt = libxml2.createPushParser(None, "<foo", 4, "test.xml") |
| 203 | ctxt.parseChunk("/>", 2, 1) |
| 204 | doc = ctxt.doc() |
| 205 | |
| 206 | doc.freeDoc()</pre> |
| 207 | <p>The context is created with a speciall call based on the |
| 208 | xmlCreatePushParser() from the C library. The first argument is an optional |
| 209 | SAX callback object, then the initial set of data, the lenght and the name of |
| 210 | the resource in case URI-References need to be computed by the parser.</p> |
| 211 | <p>Then the data are pushed using the parseChunk() method, the last call |
| 212 | setting the thrird argument terminate to 1.</p> |
| 213 | <h3>pushSAX.py:</h3> |
| 214 | <p>this test show the use of the event based parsing interfaces. In this case |
| 215 | the parser does not build a document, but provides callback information as |
| 216 | the parser makes progresses analyzing the data being provided:</p> |
| 217 | <pre>import libxml2 |
| 218 | log = "" |
| 219 | |
| 220 | class callback: |
| 221 | def startDocument(self): |
| 222 | global log |
| 223 | log = log + "startDocument:" |
| 224 | |
| 225 | def endDocument(self): |
| 226 | global log |
| 227 | log = log + "endDocument:" |
| 228 | |
| 229 | def startElement(self, tag, attrs): |
| 230 | global log |
| 231 | log = log + "startElement %s %s:" % (tag, attrs) |
| 232 | |
| 233 | def endElement(self, tag): |
| 234 | global log |
| 235 | log = log + "endElement %s:" % (tag) |
| 236 | |
| 237 | def characters(self, data): |
| 238 | global log |
| 239 | log = log + "characters: %s:" % (data) |
| 240 | |
| 241 | def warning(self, msg): |
| 242 | global log |
| 243 | log = log + "warning: %s:" % (msg) |
| 244 | |
| 245 | def error(self, msg): |
| 246 | global log |
| 247 | log = log + "error: %s:" % (msg) |
| 248 | |
| 249 | def fatalError(self, msg): |
| 250 | global log |
| 251 | log = log + "fatalError: %s:" % (msg) |
| 252 | |
| 253 | handler = callback() |
| 254 | |
| 255 | ctxt = libxml2.createPushParser(handler, "<foo", 4, "test.xml") |
| 256 | chunk = " url='tst'>b" |
| 257 | ctxt.parseChunk(chunk, len(chunk), 0) |
| 258 | chunk = "ar</foo>" |
| 259 | ctxt.parseChunk(chunk, len(chunk), 1) |
| 260 | |
| 261 | reference = "startDocument:startElement foo {'url': 'tst'}:characters: bar:endElement foo:endDocument:" |
| 262 | if log != reference: |
| 263 | print "Error got: %s" % log |
| 264 | print "Exprected: %s" % reference</pre> |
| 265 | <p>The key object in that test is the handler, it provides a number of entry |
| 266 | points which can be called by the parser as it makes progresses to indicate |
| 267 | the information set obtained. The full set of callback is larger than what |
| 268 | the callback class in that specific example implements (see the SAX |
| 269 | definition for a complete list). The wrapper will only call those supplied by |
| 270 | the object when activated. The startElement receives the names of the element |
| 271 | and a dictionnary containing the attributes carried by this element.</p> |
| 272 | <p>Also note that the reference string generated from the callback shows a |
| 273 | single character call even though the string "bar" is passed to the parser |
| 274 | from 2 different call to parseChunk()</p> |
| 275 | <h3>xpath.py:</h3> |
| 276 | <p>This is a basic test of XPath warppers support</p> |
| 277 | <pre>import libxml2 |
| 278 | |
| 279 | doc = libxml2.parseFile("tst.xml") |
| 280 | ctxt = doc.xpathNewContext() |
| 281 | res = ctxt.xpathEval("//*") |
| 282 | if len(res) != 2: |
| 283 | print "xpath query: wrong node set size" |
| 284 | sys.exit(1) |
| 285 | if res[0].name != "doc" or res[1].name != "foo": |
| 286 | print "xpath query: wrong node set value" |
| 287 | sys.exit(1) |
| 288 | doc.freeDoc() |
| 289 | ctxt.xpathFreeContext()</pre> |
| 290 | <p>This test parses a file, then create an XPath context to evaluate XPath |
| 291 | expression on it. The xpathEval() method execute an XPath query and returns |
| 292 | the result mapped in a Python way. String and numbers are natively converted, |
| 293 | and node sets are returned as a tuple of libxml2 Python nodes wrappers. Like |
| 294 | the document, the XPath context need to be freed explicitely, also not that |
| 295 | the result of the XPath query may point back to the document tree and hence |
| 296 | the document must be freed after the result of the query is used.</p> |
| 297 | <h3>xpathext.py:</h3> |
| 298 | <p>This test shows how to extend the XPath engine with functions written in |
| 299 | python:</p> |
| 300 | <pre>import libxml2 |
| 301 | |
| 302 | def foo(ctx, x): |
| 303 | return x + 1 |
| 304 | |
| 305 | doc = libxml2.parseFile("tst.xml") |
| 306 | ctxt = doc.xpathNewContext() |
| 307 | libxml2.registerXPathFunction(ctxt._o, "foo", None, foo) |
| 308 | res = ctxt.xpathEval("foo(1)") |
| 309 | if res != 2: |
| 310 | print "xpath extension failure" |
| 311 | doc.freeDoc() |
| 312 | ctxt.xpathFreeContext()</pre> |
| 313 | <p>Note how the extension function is registered with the context (but that |
| 314 | part is not yet finalized, ths may change slightly in the future).</p> |
| 315 | <h3>tstxpath.py:</h3> |
| 316 | <p>This test is similar to the previousone but shows how the extension |
| 317 | function can access the XPath evaluation context:</p> |
| 318 | <pre>def foo(ctx, x): |
| 319 | global called |
| 320 | |
| 321 | # |
| 322 | # test that access to the XPath evaluation contexts |
| 323 | # |
| 324 | pctxt = libxml2.xpathParserContext(_obj=ctx) |
| 325 | ctxt = pctxt.context() |
| 326 | called = ctxt.function() |
| 327 | return x + 1</pre> |
| 328 | <p>All the interfaces around the XPath parser(or rather evaluation) context |
| 329 | are not finalized, but it should be sufficient to do contextual work at the |
| 330 | evaluation point.</p> |
| 331 | <h3>Memory debugging:</h3> |
| 332 | <p>last but not least, all tests starts with the following prologue:</p> |
| 333 | <pre>#memory debug specific |
| 334 | libxml2.debugMemory(1) |
| 335 | </pre> |
| 336 | <p>and ends with the following epilogue:</p> |
| 337 | <pre>#memory debug specific |
| 338 | libxml2.cleanupParser() |
| 339 | if libxml2.debugMemory(1) == 0: |
| 340 | print "OK" |
| 341 | else: |
| 342 | print "Memory leak %d bytes" % (libxml2.debugMemory(1)) |
| 343 | libxml2.dumpMemory()</pre> |
| 344 | <p>Those activate the memory debugging interface of libxml2 where all |
| 345 | alloacted block in the library are tracked. The prologue then cleans up the |
| 346 | library state and checks that all allocated memory has been freed. If not it |
| 347 | calls dumpMemory() which saves that list in a <code>.memdump</code> file.</p> |
| 348 | <p><a href="bugs.html">Daniel Veillard</a></p> |
| 349 | </td></tr></table></td></tr></table></td></tr></table></td> |
| 350 | </tr></table></td></tr></table> |
| 351 | </body> |
| 352 | </html> |