Loads the named field descriptor from the pool.

    Args:
      full_name: The full name of the field descriptor to load.

    Returns:
      The field descriptor for the named field.

    Raises:
      KeyError: if the field cannot be found in the pool.

def FindFieldByName(self, full_name):
    """Loads the named field descriptor from the pool.

    Args:
      full_name: The full name of the field descriptor to load.

    Returns:
      The field descriptor for the named field.

    Raises:
      KeyError: if the field cannot be found in the pool.
    """
    full_name = _NormalizeFullyQualifiedName(full_name)
    message_name, _, field_name = full_name.rpartition('.')
    message_descriptor = self.FindMessageTypeByName(message_name)
    return message_descriptor.fields_by_name[field_name]