title: ValueError: could not convert string to float: pythonGUI
body: <pre><code>costOfItem = (Item1 * 10) + (Item2 * 20)\
                                + (Item3 * 30) + (Item4 * 40) + (Item5 * 50) + (Item6 * 60) + (Item7* 70) + (Item8* 80)
                   SubTotalofITEMS = "Rs.", str('%.2f'% costOfItem)
  
                   SubTotal.set(SubTotalofITEMS)
                   Tax="Rs.", str('%.2f'% ((costOfItem) * 0.08))
                   GSTTax.set(Tax)
                   TTax = ((costOfItem) * 0.08)
  
                   TCost = "Rs.", ('%.2f'% (costOfItem + TTax))
                   TotalCost.set(TCost)
  </code></pre>
  
  <p>I'll Makaing Python GUI Restront billing management system.But I'M facing problem to costofItem in calculation.....</p>
  
  <pre><code> **strong text**
     Error showing 
      t__.py", line 1705, in __call__
          return self.func(*args)
        File "C:\Users\Lenovo\Desktop\Py.Billing system - Copy.py", line 252, in costOfItem
          Item1=float(Tea.get())
      ValueError: could not convert string to float: 
  </code></pre>