Fetches the column number (0 indexed).

    Args:
      column: A string, column to fetch the index of.

    Returns:
      An int, the row index number.

    Raises:
      ValueError: The specified column was not found.

def index(self, column):  # pylint: disable=C6409
        """Fetches the column number (0 indexed).

    Args:
      column: A string, column to fetch the index of.

    Returns:
      An int, the row index number.

    Raises:
      ValueError: The specified column was not found.
    """
        for i, key in enumerate(self._keys):
            if key == column:
                return i
        raise ValueError('Column "%s" not found.' % column)