code: def get_mimetype(self):
          
          if hasattr(self, '_mimetype'):
              if (isinstance(self._mimetype, (tuple, list,)) and
                  len(self._mimetype) == 2):
                  return self._mimetype
              else:
                  raise NodeError('given _mimetype attribute must be an 2 '
                                 'element list or tuple')
  
          mtype, encoding = mimetypes.guess_type(self.name)
  
          if mtype is None:
              if self.is_binary:
                  mtype = 'application/octet-stream'
                  encoding = None
              else:
                  mtype = 'text/plain'
                  encoding = None
          return mtype, encoding
docs: Mimetype is calculated based on the file's content. If ``_mimetype``
          attribute is available, it will be returned (backends which store
          mimetypes or can easily recognize them, should set this private
          attribute to indicate that type should *NOT* be calculated).