code: def _get_content_type(self, content_type, filename=None):
          
          if content_type is None:
              content_type = self.content_type
  
          if content_type is None and filename is not None:
              content_type, _ = mimetypes.guess_type(filename)
  
          if content_type is None:
              content_type = _DEFAULT_CONTENT_TYPE
  
          return content_type
docs: Determine the content type from the current object.
  
          The return value will be determined in order of precedence:
  
          - The value passed in to this method (if not :data:`None`)
          - The value stored on the current blob
          - The default value ('application/octet-stream')
  
          :type content_type: str
          :param content_type: (Optional) type of content.
  
          :type filename: str
          :param filename: (Optional) The name of the file where the content
                           is stored.
  
          :rtype: str
          :returns: Type of content gathered from the object.