Source Code for Module ndg.xacml.parsers.etree.expressionreader

 1  """NDG XACML ElementTree based reader for Expression type 
 2   
 3  NERC DataGrid 
 4  """ 
 5  __author__ = "P J Kershaw" 
 6  __date__ = "18/03/10" 
 7  __copyright__ = "(C) 2010 Science and Technology Facilities Council" 
 8  __contact__ = "Philip.Kershaw@stfc.ac.uk" 
 9  __license__ = "BSD - see LICENSE file in top-level directory" 
10  __contact__ = "Philip.Kershaw@stfc.ac.uk" 
11  __revision__ = "$Id: expressionreader.py 7955 2011-12-21 18:29:45Z rwilkinson $" 
12  from abc import abstractmethod 
13   
14  from ndg.xacml.core.expression import Expression 
15  from ndg.xacml.parsers import XMLParseError 
16  from ndg.xacml.parsers.etree import QName 
17  from ndg.xacml.parsers.etree.reader import ETreeAbstractReader 
18   
19   
20 -class ExpressionReader(ETreeAbstractReader): 
21      '''ElementTree based XACML Expression type parser 
22       
23      @cvar TYPE: XACML type to instantiate from parsed object 
24      @type TYPE: abc.ABCMeta 
25      ''' 
26      TYPE = Expression 
27       
28 -    def __call__(self, obj, common): 
29          """Parse Expression object 
30           
31          @param obj: input object to parse 
32          @type obj: ElementTree Element, or stream object 
33          @return: new XACML expression instance 
34          @rtype: ndg.xacml.core.expression.Expression derived type  
35          @raise XMLParseError: error reading element                
36          """ 
37          elem = super(ExpressionReader, self)._parse(obj) 
38           
39          xacmlType = self.__class__.TYPE 
40          expression = xacmlType() 
41           
42          localName = QName.getLocalPart(elem.tag) 
43          if localName != xacmlType.ELEMENT_LOCAL_NAME: 
44              raise XMLParseError("No \"%s\" element found" %  
45                                  xacmlType.ELEMENT_LOCAL_NAME) 
46               
47          # Unpack *required* attributes from top-level element 
48          attributeValues = [] 
49          for attributeName in (xacmlType.DATA_TYPE_ATTRIB_NAME,): 
50              attributeValue = elem.attrib.get(attributeName) 
51              if attributeValue is None: 
52                  raise XMLParseError('No "%s" attribute found in "%s" element' % 
53                                      (attributeName,  
54                                       xacmlType.ELEMENT_LOCAL_NAME)) 
55                   
56              attributeValues.append(attributeValue) 
57                
58          expression.dataType, = attributeValues 
59                      
60          self._parseExtension(elem, expression) 
61           
62          return expression 
63           
64      @abstractmethod 
65 -    def _parseExtension(self, elem, expression): 
66          """Derived classes should implement this method to read any remaining 
67          attributes and elements specific to their type 
68           
69          @param elem: ElementTree XML element 
70          @type elem: xml.etree.Element 
71           
72          @param expression: attribute selector to be updated with parsed 
73          values 
74          @type expression: ndg.xacml.core.attributevalue.AttributeValue 
75           
76           
77          @raise NotImplementedError: Derived classes should implement 
78          """ 
79          raise NotImplementedError() 
80             
81  # Set up new class as an abstract base itself              
82  ETreeAbstractReader.register(ExpressionReader) 
83