text: # Copyright 2010 Google Inc.
  #
  # Permission is hereby granted, free of charge, to any person obtaining a
  # copy of this software and associated documentation files (the
  # "Software"), to deal in the Software without restriction, including
  # without limitation the rights to use, copy, modify, merge, publish, dis-
  # tribute, sublicense, and/or sell copies of the Software, and to permit
  # persons to whom the Software is furnished to do so, subject to the fol-
  # lowing conditions:
  #
  # The above copyright notice and this permission notice shall be included
  # in all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  # OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABIL-
  # ITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
  # SHALL THE AUTHOR BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  # WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  # IN THE SOFTWARE.
  
  
  """
  Implements plugin related api.
  
  To define a new plugin just subclass Plugin, like this.
  
  class AuthPlugin(Plugin):
      pass
  
  Then start creating subclasses of your new plugin.
  
  class MyFancyAuth(AuthPlugin):
      capability = ['sign', 'vmac']
  
  The actual interface is duck typed.
  """
  
  import glob
  import imp
  import os.path
  
  
  class Plugin(object):
      """Base class for all plugins."""
  
      capability = []
  
      @classmethod
      def is_capable(cls, requested_capability):
          """Returns true if the requested capability is supported by this plugin
          """
          for c in requested_capability:
              if c not in cls.capability:
                  return False
          return True
  
  
  def get_plugin(cls, requested_capability=None):
      if not requested_capability:
          requested_capability = []
      result = []
      for handler in cls.__subclasses__():
          if handler.is_capable(requested_capability):
              result.append(handler)
      return result
  
  
  def _import_module(filename):
      (path, name) = os.path.split(filename)
      (name, ext) = os.path.splitext(name)
  
      (file, filename, data) = imp.find_module(name, [path])
      try:
          return imp.load_module(name, file, filename, data)
      finally:
          if file:
              file.close()
  
  _plugin_loaded = False
  
  
  def load_plugins(config):
      global _plugin_loaded
      if _plugin_loaded:
          return
      _plugin_loaded = True
  
      if not config.has_option('Plugin', 'plugin_directory'):
          return
      directory = config.get('Plugin', 'plugin_directory')
      for file in glob.glob(os.path.join(directory, '*.py')):
          _import_module(file)
  