code: def projection(self, plain_src_name):
          
          mapped = self.lookup(plain_src_name)
          if not mapped:
              return None
          fields = mapped.include_fields or mapped.exclude_fields
          if fields:
              include = 1 if mapped.include_fields else 0
              return dict((field, include) for field in fields)
          return None
docs: Return the projection for the given source namespace.