title: 'UpgradeApp' object has no attribute '_tk'
body: <p>I have added the some value in Entry widget and on submitting button am trying to fetch that value using get function. But em getting following error please anybody help me on this.</p>
  
  <p><code>'UpgradeApp' object has no attribute '_tk'</code></p>
  
  <pre><code>class UpgradeApp:
      def __init__(self):
          self.root = tk.Tk()
          self.newvalue = tk.StringVar
          self.input()
  
      def input(self):
          tk.Label(self.root, text="IP Address", relief="groove" ).grid(row=0, columnspan =3, sticky = tk.NSEW)
          ip_entry = ttk.Entry(self.root, textvariable = self.newvalue)
          ip_entry.grid(column=3, row=0, sticky=tk.W, padx=5, pady=5)
          connect = tk.Button(self.root, text="conn", relief="groove", command= self.onclickconnect)
          connect.grid(row=1, padx = 5, pady = 5, column = 0)
          #connect.bind('&lt;Button-1&gt;',self.onclick)
          tk.Button(self.root, text="dlt", relief="groove").grid(row=1, padx = 5, pady = 5, column =1)
          tk.Button(self.root, text="clr", relief="groove").grid(row=1, padx = 5, pady = 5, column =2)
  
      def onclickconnect(self):
          ip = self.newvalue.get(self)
          Node(ip,True, True)
  
  if __name__ == "__main__":
      app = UpgradeApp()
      app.root.mainloop()
  </code></pre>