title: tkinter python 3.4 set zero if DoubleVar or IntVar is empty
body: <p>I am trying to set a text-box or EntryBox to 0 if this entry box is empty
  I can do it if the entrybox's textvariable is a String, but I cant if is a DoubleVar or an IntVar</p>
  
  <p>here is my code</p>
  
  <pre><code>mGui = Tk()
  mGui.title("GUI")
  mGui.geometry('1250x650+10+10')
  
  def mCheck():
    if len(name1.get()) == 0:
      name1.set('noidea')
      mGui.update()
    if (len(name2.get()) == 0):
      name2.set('nofkidea')
      mGui.update()
    if (value1.get()== Empty or (len(str(value2.get()))=0) or (len(str(float(value2.get()))) == 0)):
      name2.set(10)
      mGui.update()
    if (value2.get()== None or (len(str(value2.get()))=0) or (len(str(float(value2.get()))) == 0)):
      name2.set(99999)
      mGui.update()
  
  value1 = DoubleVar()
  value2 = DoubleVar()
  name1 = StringVar()
  name2 = StringVar()
  mButtonLoad = Button(mGui, text = "check", command = mCheck, fg = 'Red').place(x=550,y=140)
  tText1 = Entry(mGui, textvariable = name1).place(x=10,y=80)
  tText2 = Entry(mGui, textvariable = name2).place(x=10,y=100)
  vText1 = Entry(mGui, textvariable = value1).place(x=200,y=80)
  vText2 = Entry(mGui, textvariable = value2).place(x=200,y=100)
  
  mGui.after(1, mGui.update)
  mGui.mainloop()
  </code></pre>
  
  <p>I am getting this error when I Try to set the DoubleVar textboxes to 0 if these ones are empty</p>
  
  <pre><code>ValueError: could not convert string to float: 
  </code></pre>