Selecting/Invoking Menubuttons in python Tkinter -

i trying create menu calls sql database life expectancy data across world. i'm having trouble menubutton, want set first value ("no region selected") initial value. there 3 things want: how set value default (ideally equivalent of invoked normal radiobuttons), there better want option menubutton, , there decent web page can me (tutorialspoint got me in initial direction, unless i'm looking in wrong places, can't find how select , invoke radiobuttons in menubutton).

ideally, i'd advise on how not have menuoptions stretch everywhere too. limit of 20?

here's of stripped down piece of code.

edit: i've found solution select/invoke issues. mb.menu.invoke(0)

from tkinter import * import tkmessagebox import tkinter import sqlite3   def selectstuff():     selectionregion = str(countryvar.get())     mb.config(text = selectionregion)    sqllocation = 'alldata/lifeexpectency.sqlite' sqldb = sqlite3.connect(sqllocation)  cursor = sqldb.cursor()  root = tk() framecountry = frame(root) framecountry.pack() stringcountry= stringvar()         labelcountry = label(framecountry, textvariable=stringcountry) stringcountry.set("select region") labelcountry.pack() '''-------------------------------''' mb =  menubutton ( framecountry, relief=raised, activebackground="white") mb.grid() mb.menu  =  menu ( mb, tearoff = 0 ) mb["menu"]  =  mb.menu sql1 = "select country total_lifespan"  countryvar = stringvar()  mb.menu.add_radiobutton  ( label="no region selected", variable =countryvar,                            value = "no region selected", command =selectstuff)  try:     cursor.execute(sql1)     results = cursor.fetchall()     row in results:         mb.menu.add_radiobutton  ( label=row, variable =countryvar, value = row,                                    command =selectstuff) except:     print "error: unable retrieve data."   mb.pack() '''-------------------------------''' #edit:  mb.menu.invoke(0) #/edit: root.mainloop()  sqldb.close()