如何解决“没有足够的值要解包（预期2，得到1）”错误？

Question

以下是我的代码：

 <asp:UpdatePanel ID="UpdatePanel" runat="server">
                <ContentTemplate>
                    <asp:DropDownList ID="dptest" OnSelectedIndexChanged="dptest_OnSelectedIndexChanged" runat="server"/>
                    <asp:GridView ID="testID" runat="server" CellPadding="3" BackColor="White" BorderColor="#CCCCCC" BorderStyle="None" BorderWidth="1px">
                        <FooterStyle BackColor="White" ForeColor="#000066"/>
                        <HeaderStyle Width="100px" BackColor="#006699" Font-Bold="True" ForeColor="White"/>
                        <PagerStyle BackColor="White" ForeColor="#000066" HorizontalAlign="Left"/>
                        <RowStyle Width="100px" ForeColor="#000066"/>
                        <SelectedRowStyle BackColor="#669999" Font-Bold="True" ForeColor="White"/>
                        <SortedAscendingCellStyle BackColor="#F1F1F1"/>
                        <SortedAscendingHeaderStyle BackColor="#007DBB"/>
                        <SortedDescendingCellStyle BackColor="#CAC9C9"/>
                        <SortedDescendingHeaderStyle BackColor="#00547E"/>

                    </asp:GridView>
                </ContentTemplate>

            </asp:UpdatePanel>

当我使用pygsheets将a1的值写入Google表格时；我遇到以下错误

a1 = df[df['email'] == 'amazon@tjori.com'].groupby('email')['revenue_after_tax'].sum()