一直没找到如何将tkinter 对话框里面的OptionMenu下拉内容随着我选择的xlsx文件的表格动态变化，搞了很久终于在一个示例中发现了用法，搞定了。
下面简单截取重点内容如下：
sheetmenu = tk.OptionMenu(root, v1, '空')
sheetmenu.grid(padx=4, row=8, column=2, columnspan=2)
button_selectfile = tk.Button(root, text='Select XLSX File', width=20, height=2, font=('宋体', 16), relief='flat', background='#C0C0C0', command=lambda: selectfile())
button_selectfile.grid(padx=4, row=7, column=1, columnspan=3)
def selectfile():
global name
global v1
name = tk.filedialog.askopenfilename(filetypes=[('XLSX', '*.xlsx')])
filename.set(name)
if name != '':
wb = openpyxl.load_workbook(name)
sheets = wb.get_sheet_names()
menu = sheetmenu['menu']
# Clear the menu.
menu.delete(0, 'end')
for st in sheets:
# Add menu items
menu.add_command(label=st, command=lambda x=st: v1.set(x))
v1.set('请选择...')
