code: def create_filter(self, propname=None, comparitor=None, value=None):
          
          if propname is None or comparitor is None or value is None:
              return None
  
          rfilter = self.create_element('ogc', 'Filter')
          ftype = None
          if comparitor == '==':
              ftype = 'PropertyIsEqualTo'
          elif comparitor == '<=':
              ftype = 'PropertyIsLessThanOrEqualTo'
          elif comparitor == '<':
              ftype = 'PropertyIsLessThan'
          elif comparitor == '>=':
              ftype = 'PropertyIsGreaterThanOrEqualTo'
          elif comparitor == '>':
              ftype = 'PropertyIsGreaterThan'
          elif comparitor == '!=':
              ftype = 'PropertyIsNotEqualTo'
          elif comparitor == '%':
              ftype = 'PropertyIsLike'
  
          if not ftype is None:
              prop = PropertyCriterion(rfilter, ftype)
              prop.PropertyName = propname
              if not value is None:
                  prop.Literal = value
              setattr(rfilter, ftype, prop)
  
          return rfilter
docs: Create a L{Filter} for this rule. The property name, comparitor, and value
          are required to create a valid Filter.
  
          @type    propname: string
          @param   propname: The name of the property to filter.
          @type  comparitor: string
          @param comparitor: The comparison to perform on the property. One of
              "!=", "<", "<=", "=", ">=", ">", and "%" is required.
          @type       value: string
          @param      value: The value of the property to compare against.
          @rtype: L{Filter}
          @return: A new filter attached to this Rule.