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authorLibravatarLibravatar Biswakalyan Bhuyan <biswa@surgot.in> 2022-11-13 23:46:45 +0530
committerLibravatarLibravatar Biswakalyan Bhuyan <biswa@surgot.in> 2022-11-13 23:46:45 +0530
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+"""The ``lxml.isoschematron`` package implements ISO Schematron support on top
+of the pure-xslt 'skeleton' implementation.
+"""
+
+import sys
+import os.path
+from lxml import etree as _etree # due to validator __init__ signature
+
+
+# some compat stuff, borrowed from lxml.html
+try:
+ unicode
+except NameError:
+ # Python 3
+ unicode = str
+try:
+ basestring
+except NameError:
+ # Python 3
+ basestring = str
+
+
+__all__ = ['extract_xsd', 'extract_rng', 'iso_dsdl_include',
+ 'iso_abstract_expand', 'iso_svrl_for_xslt1',
+ 'svrl_validation_errors', 'schematron_schema_valid',
+ 'stylesheet_params', 'Schematron']
+
+
+# some namespaces
+#FIXME: Maybe lxml should provide a dedicated place for common namespace
+#FIXME: definitions?
+XML_SCHEMA_NS = "http://www.w3.org/2001/XMLSchema"
+RELAXNG_NS = "http://relaxng.org/ns/structure/1.0"
+SCHEMATRON_NS = "http://purl.oclc.org/dsdl/schematron"
+SVRL_NS = "http://purl.oclc.org/dsdl/svrl"
+
+
+# some helpers
+_schematron_root = '{%s}schema' % SCHEMATRON_NS
+_xml_schema_root = '{%s}schema' % XML_SCHEMA_NS
+_resources_dir = os.path.join(os.path.dirname(__file__), 'resources')
+
+
+# the iso-schematron skeleton implementation steps aka xsl transformations
+extract_xsd = _etree.XSLT(_etree.parse(
+ os.path.join(_resources_dir, 'xsl', 'XSD2Schtrn.xsl')))
+extract_rng = _etree.XSLT(_etree.parse(
+ os.path.join(_resources_dir, 'xsl', 'RNG2Schtrn.xsl')))
+iso_dsdl_include = _etree.XSLT(_etree.parse(
+ os.path.join(_resources_dir, 'xsl', 'iso-schematron-xslt1',
+ 'iso_dsdl_include.xsl')))
+iso_abstract_expand = _etree.XSLT(_etree.parse(
+ os.path.join(_resources_dir, 'xsl', 'iso-schematron-xslt1',
+ 'iso_abstract_expand.xsl')))
+iso_svrl_for_xslt1 = _etree.XSLT(_etree.parse(
+ os.path.join(_resources_dir,
+ 'xsl', 'iso-schematron-xslt1', 'iso_svrl_for_xslt1.xsl')))
+
+
+# svrl result accessors
+svrl_validation_errors = _etree.XPath(
+ '//svrl:failed-assert', namespaces={'svrl': SVRL_NS})
+
+
+# RelaxNG validator for schematron schemas
+schematron_schema_valid = _etree.RelaxNG(
+ file=os.path.join(_resources_dir, 'rng', 'iso-schematron.rng'))
+
+
+def stylesheet_params(**kwargs):
+ """Convert keyword args to a dictionary of stylesheet parameters.
+ XSL stylesheet parameters must be XPath expressions, i.e.:
+
+ * string expressions, like "'5'"
+ * simple (number) expressions, like "5"
+ * valid XPath expressions, like "/a/b/text()"
+
+ This function converts native Python keyword arguments to stylesheet
+ parameters following these rules:
+ If an arg is a string wrap it with XSLT.strparam().
+ If an arg is an XPath object use its path string.
+ If arg is None raise TypeError.
+ Else convert arg to string.
+ """
+ result = {}
+ for key, val in kwargs.items():
+ if isinstance(val, basestring):
+ val = _etree.XSLT.strparam(val)
+ elif val is None:
+ raise TypeError('None not allowed as a stylesheet parameter')
+ elif not isinstance(val, _etree.XPath):
+ val = unicode(val)
+ result[key] = val
+ return result
+
+
+# helper function for use in Schematron __init__
+def _stylesheet_param_dict(paramsDict, kwargsDict):
+ """Return a copy of paramsDict, updated with kwargsDict entries, wrapped as
+ stylesheet arguments.
+ kwargsDict entries with a value of None are ignored.
+ """
+ # beware of changing mutable default arg
+ paramsDict = dict(paramsDict)
+ for k, v in kwargsDict.items():
+ if v is not None: # None values do not override
+ paramsDict[k] = v
+ paramsDict = stylesheet_params(**paramsDict)
+ return paramsDict
+
+
+class Schematron(_etree._Validator):
+ """An ISO Schematron validator.
+
+ Pass a root Element or an ElementTree to turn it into a validator.
+ Alternatively, pass a filename as keyword argument 'file' to parse from
+ the file system.
+
+ Schematron is a less well known, but very powerful schema language.
+ The main idea is to use the capabilities of XPath to put restrictions on
+ the structure and the content of XML documents.
+
+ The standard behaviour is to fail on ``failed-assert`` findings only
+ (``ASSERTS_ONLY``). To change this, you can either pass a report filter
+ function to the ``error_finder`` parameter (e.g. ``ASSERTS_AND_REPORTS``
+ or a custom ``XPath`` object), or subclass isoschematron.Schematron for
+ complete control of the validation process.
+
+ Built on the Schematron language 'reference' skeleton pure-xslt
+ implementation, the validator is created as an XSLT 1.0 stylesheet using
+ these steps:
+
+ 0) (Extract from XML Schema or RelaxNG schema)
+ 1) Process inclusions
+ 2) Process abstract patterns
+ 3) Compile the schematron schema to XSLT
+
+ The ``include`` and ``expand`` keyword arguments can be used to switch off
+ steps 1) and 2).
+ To set parameters for steps 1), 2) and 3) hand parameter dictionaries to the
+ keyword arguments ``include_params``, ``expand_params`` or
+ ``compile_params``.
+ For convenience, the compile-step parameter ``phase`` is also exposed as a
+ keyword argument ``phase``. This takes precedence if the parameter is also
+ given in the parameter dictionary.
+
+ If ``store_schematron`` is set to True, the (included-and-expanded)
+ schematron document tree is stored and available through the ``schematron``
+ property.
+ If ``store_xslt`` is set to True, the validation XSLT document tree will be
+ stored and can be retrieved through the ``validator_xslt`` property.
+ With ``store_report`` set to True (default: False), the resulting validation
+ report document gets stored and can be accessed as the ``validation_report``
+ property.
+
+ Here is a usage example::
+
+ >>> from lxml import etree
+ >>> from lxml.isoschematron import Schematron
+
+ >>> schematron = Schematron(etree.XML('''
+ ... <schema xmlns="http://purl.oclc.org/dsdl/schematron" >
+ ... <pattern id="id_only_attribute">
+ ... <title>id is the only permitted attribute name</title>
+ ... <rule context="*">
+ ... <report test="@*[not(name()='id')]">Attribute
+ ... <name path="@*[not(name()='id')]"/> is forbidden<name/>
+ ... </report>
+ ... </rule>
+ ... </pattern>
+ ... </schema>'''),
+ ... error_finder=Schematron.ASSERTS_AND_REPORTS)
+
+ >>> xml = etree.XML('''
+ ... <AAA name="aaa">
+ ... <BBB id="bbb"/>
+ ... <CCC color="ccc"/>
+ ... </AAA>
+ ... ''')
+
+ >>> schematron.validate(xml)
+ False
+
+ >>> xml = etree.XML('''
+ ... <AAA id="aaa">
+ ... <BBB id="bbb"/>
+ ... <CCC/>
+ ... </AAA>
+ ... ''')
+
+ >>> schematron.validate(xml)
+ True
+ """
+
+ # libxml2 error categorization for validation errors
+ _domain = _etree.ErrorDomains.SCHEMATRONV
+ _level = _etree.ErrorLevels.ERROR
+ _error_type = _etree.ErrorTypes.SCHEMATRONV_ASSERT
+
+ # convenience definitions for common behaviours
+ ASSERTS_ONLY = svrl_validation_errors # Default
+ ASSERTS_AND_REPORTS = _etree.XPath(
+ '//svrl:failed-assert | //svrl:successful-report',
+ namespaces={'svrl': SVRL_NS})
+
+ def _extract(self, element):
+ """Extract embedded schematron schema from non-schematron host schema.
+ This method will only be called by __init__ if the given schema document
+ is not a schematron schema by itself.
+ Must return a schematron schema document tree or None.
+ """
+ schematron = None
+ if element.tag == _xml_schema_root:
+ schematron = self._extract_xsd(element)
+ elif element.nsmap[element.prefix] == RELAXNG_NS:
+ # RelaxNG does not have a single unique root element
+ schematron = self._extract_rng(element)
+ return schematron
+
+ # customization points
+ # etree.XSLT objects that provide the extract, include, expand, compile
+ # steps
+ _extract_xsd = extract_xsd
+ _extract_rng = extract_rng
+ _include = iso_dsdl_include
+ _expand = iso_abstract_expand
+ _compile = iso_svrl_for_xslt1
+
+ # etree.xpath object that determines input document validity when applied to
+ # the svrl result report; must return a list of result elements (empty if
+ # valid)
+ _validation_errors = ASSERTS_ONLY
+
+ def __init__(self, etree=None, file=None, include=True, expand=True,
+ include_params={}, expand_params={}, compile_params={},
+ store_schematron=False, store_xslt=False, store_report=False,
+ phase=None, error_finder=ASSERTS_ONLY):
+ super(Schematron, self).__init__()
+
+ self._store_report = store_report
+ self._schematron = None
+ self._validator_xslt = None
+ self._validation_report = None
+ if error_finder is not self.ASSERTS_ONLY:
+ self._validation_errors = error_finder
+
+ # parse schema document, may be a schematron schema or an XML Schema or
+ # a RelaxNG schema with embedded schematron rules
+ root = None
+ try:
+ if etree is not None:
+ if _etree.iselement(etree):
+ root = etree
+ else:
+ root = etree.getroot()
+ elif file is not None:
+ root = _etree.parse(file).getroot()
+ except Exception:
+ raise _etree.SchematronParseError(
+ "No tree or file given: %s" % sys.exc_info()[1])
+ if root is None:
+ raise ValueError("Empty tree")
+ if root.tag == _schematron_root:
+ schematron = root
+ else:
+ schematron = self._extract(root)
+ if schematron is None:
+ raise _etree.SchematronParseError(
+ "Document is not a schematron schema or schematron-extractable")
+ # perform the iso-schematron skeleton implementation steps to get a
+ # validating xslt
+ if include:
+ schematron = self._include(schematron, **include_params)
+ if expand:
+ schematron = self._expand(schematron, **expand_params)
+ if not schematron_schema_valid(schematron):
+ raise _etree.SchematronParseError(
+ "invalid schematron schema: %s" %
+ schematron_schema_valid.error_log)
+ if store_schematron:
+ self._schematron = schematron
+ # add new compile keyword args here if exposing them
+ compile_kwargs = {'phase': phase}
+ compile_params = _stylesheet_param_dict(compile_params, compile_kwargs)
+ validator_xslt = self._compile(schematron, **compile_params)
+ if store_xslt:
+ self._validator_xslt = validator_xslt
+ self._validator = _etree.XSLT(validator_xslt)
+
+ def __call__(self, etree):
+ """Validate doc using Schematron.
+
+ Returns true if document is valid, false if not.
+ """
+ self._clear_error_log()
+ result = self._validator(etree)
+ if self._store_report:
+ self._validation_report = result
+ errors = self._validation_errors(result)
+ if errors:
+ if _etree.iselement(etree):
+ fname = etree.getroottree().docinfo.URL or '<file>'
+ else:
+ fname = etree.docinfo.URL or '<file>'
+ for error in errors:
+ # Does svrl report the line number, anywhere? Don't think so.
+ self._append_log_message(
+ domain=self._domain, type=self._error_type,
+ level=self._level, line=0,
+ message=_etree.tostring(error, encoding='unicode'),
+ filename=fname)
+ return False
+ return True
+
+ @property
+ def schematron(self):
+ """ISO-schematron schema document (None if object has been initialized
+ with store_schematron=False).
+ """
+ return self._schematron
+
+ @property
+ def validator_xslt(self):
+ """ISO-schematron skeleton implementation XSLT validator document (None
+ if object has been initialized with store_xslt=False).
+ """
+ return self._validator_xslt
+
+ @property
+ def validation_report(self):
+ """ISO-schematron validation result report (None if result-storing has
+ been turned off).
+ """
+ return self._validation_report