Source Code for Module ndg.xacml.utils.factory

  1  """ 
  2  Class Factory 
  3   
  4  NERC DataGrid project 
  5  """ 
  6  __author__ = "Philip Kershaw" 
  7  __date__ = "15/02/10" 
  8  __copyright__ = "(C) 2010 Science and Technology Facilities Council" 
  9  __license__ = "BSD - see LICENSE file in top-level directory" 
 10  __contact__ = "Philip.Kershaw@stfc.ac.uk" 
 11  __revision__ = '$Id: factory.py 7696 2010-11-03 08:57:41Z pjkersha $' 
 12  import traceback 
 13  import logging, os, sys 
 14  log = logging.getLogger(__name__) 
 15   
 16   
 17 -def importModuleObject(moduleName, objectName=None, objectType=None): 
 18      '''Import from a string module name and object name.  Object can be 
 19      any entity contained in a module 
 20       
 21      @param moduleName: Name of module containing the class 
 22      @type moduleName: str  
 23      @param objectName: Name of the class to import.  If none is given, the  
 24      class name will be assumed to be the last component of modulePath 
 25      @type objectName: str 
 26      @rtype: class object 
 27      @return: imported class''' 
 28      if objectName is None: 
 29          if ':' in moduleName: 
 30              # Support Paste style import syntax with rhs of colon denoting  
 31              # module content to import 
 32              _moduleName, objectName = moduleName.rsplit(':', 1) 
 33              if '.' in objectName: 
 34                  objectName = objectName.split('.') 
 35          else:  
 36              _moduleName, objectName = moduleName.rsplit('.', 1) 
 37      else: 
 38          _moduleName = moduleName 
 39           
 40      if isinstance(objectName, basestring): 
 41          objectName = [objectName] 
 42       
 43      module = __import__(_moduleName, globals(), locals(), []) 
 44      components = _moduleName.split('.') 
 45      try: 
 46          for component in components[1:]: 
 47              module = getattr(module, component) 
 48      except AttributeError: 
 49          raise AttributeError("Error importing %r: %s" % 
 50                               (objectName[0], traceback.format_exc())) 
 51   
 52      importedObject = module 
 53      for i in objectName: 
 54          importedObject = getattr(importedObject, i) 
 55   
 56      # Check class inherits from a base class 
 57      if objectType and not issubclass(importedObject, objectType): 
 58          raise TypeError("Specified class %r must be derived from %r; got %r" % 
 59                          (objectName, objectType, importedObject)) 
 60       
 61      log.info('Imported %r from module %r', objectName[0], _moduleName) 
 62      return importedObject 
 63   
 64   
 65 -def callModuleObject(moduleName, objectName=None, moduleFilePath=None,  
 66                       objectType=None, objectArgs=None, objectProperties=None): 
 67      ''' 
 68      Create and return an instance of the specified class or invoke callable 
 69      @param moduleName: Name of module containing the class 
 70      @type moduleName: str  
 71      @param objectName: Name of the class to instantiate.  May be None in  
 72      which case, the class name is parsed from the moduleName last element 
 73      @type objectName: str 
 74      @param moduleFilePath: Path to the module - if unset, assume module on  
 75      system path already 
 76      @type moduleFilePath: str 
 77      @param objectProperties: dict of properties to use when instantiating the  
 78      class 
 79      @type objectProperties: dict 
 80      @param objectType: expected type for the object to instantiate - to  
 81      enforce use of specific interfaces  
 82      @type objectType: object 
 83      @return: object - instance of the class specified  
 84      ''' 
 85       
 86      # ensure that properties is a dict - NB, it may be passed in as a null 
 87      # value which can override the default val 
 88      if not objectProperties: 
 89          objectProperties = {} 
 90   
 91      if not objectArgs: 
 92          objectArgs = () 
 93   
 94      # variable to store original state of the system path 
 95      sysPathBak = None 
 96      try: 
 97          try: 
 98              # Module file path may be None if the new module to be loaded 
 99              # can be found in the existing system path             
100              if moduleFilePath: 
101                  if not os.path.exists(moduleFilePath): 
102                      raise IOError("Module file path '%s' doesn't exist" %  
103                                    moduleFilePath) 
104                             
105                  # Temporarily extend system path ready for import 
106                  sysPathBak = sys.path 
107                             
108                  sys.path.append(moduleFilePath) 
109   
110               
111              # Import module name specified in properties file 
112              importedObject = importModuleObject(moduleName,  
113                                                  objectName=objectName, 
114                                                  objectType=objectType) 
115          finally: 
116              # revert back to original sys path, if necessary 
117              # NB, python requires the use of a try/finally OR a try/except  
118              # block - not both combined 
119              if sysPathBak: 
120                  sys.path = sysPathBak 
121                               
122      except Exception, e: 
123          log.debug('%r module import raised %r type exception: %s',  
124                    moduleName, e.__class__, traceback.format_exc()) 
125          raise  
126   
127      # Instantiate class 
128      if objectArgs: 
129          object = importedObject(*objectArgs, **objectProperties) 
130      else: 
131          object = importedObject(**objectProperties) 
132           
133      return object 
134