code: def find_service_references(
          self, clazz=None, ldap_filter=None, only_one=False
      ):
          
          with self.__svc_lock:
              if clazz is None and ldap_filter is None:
                  # Return a sorted copy of the keys list
                  # Do not return None, as the whole content was required
                  return sorted(self.__svc_registry.keys())
  
              if hasattr(clazz, "__name__"):
                  # Escape the type name
                  clazz = ldapfilter.escape_LDAP(clazz.__name__)
              elif is_string(clazz):
                  # Escape the class name
                  clazz = ldapfilter.escape_LDAP(clazz)
  
              if clazz is None:
                  # Directly use the given filter
                  refs_set = sorted(self.__svc_registry.keys())
              else:
                  try:
                      # Only for references with the given specification
                      refs_set = iter(self.__svc_specs[clazz])
                  except KeyError:
                      # No matching specification
                      return None
  
              # Parse the filter
              try:
                  new_filter = ldapfilter.get_ldap_filter(ldap_filter)
              except ValueError as ex:
                  raise BundleException(ex)
  
              if new_filter is not None:
                  # Prepare a generator, as we might not need a complete
                  # walk-through
                  refs_set = (
                      ref
                      for ref in refs_set
                      if new_filter.matches(ref.get_properties())
                  )
  
              if only_one:
                  # Return the first element in the list/generator
                  try:
                      return [next(refs_set)]
                  except StopIteration:
                      # No match
                      return None
  
              # Get all the matching references
              return list(refs_set) or None
docs: Finds all services references matching the given filter.
  
          :param clazz: Class implemented by the service
          :param ldap_filter: Service filter
          :param only_one: Return the first matching service reference only
          :return: A list of found references, or None
          :raise BundleException: An error occurred looking for service
                                  references