def y_label(self, y_label=None):
if y_label is None:<EOL><INDENT>return self._y_label<EOL><DEDENT>else:<EOL><INDENT>if not isinstance(y_label, str):<EOL><INDENT>raise TypeError("<STR_LIT>" % str(y_label))<EOL><DEDENT>self._y_label = y_label<EOL><DEDENT>
Returns or sets (if a value is provided) the chart's y-axis label.

        :param str y_label: If given, the chart's y_label will be set to this.
        :rtype: ``str``