title: TypeError: unsupported operand type(s) for 'Instance' and 'Int'
body: <p>I am trying to apply the PQ formula in Python 2.7. </p>
  
  <p>I'll just post a small bit of the code (where the problem appears to be coming from) here, and I'll link the long version as a pasteboard link.</p>
  
  <pre><code>etiquette2=Label(eqGroup,text="ax^2 + bx + c")
  etiquette2.pack(padx=10,pady=10,expand=True,fill=BOTH)
  etiquette3=Label(eqGroup,text="Please enter a value for a")
  etiquette3.pack(padx=10,pady=10,expand=True,fill=BOTH)
  input1=Entry(eqGroup,width=10)
  input1.pack()
  etiquette4=Label(eqGroup,text="Please enter a value for b")
  etiquette4.pack(padx=10,pady=10,expand=True,fill=BOTH)
  input2=Entry(eqGroup,width=10)
  input2.pack()
  etiquette5=Label(eqGroup,text="Please enter a value for c")
  etiquette5.pack(padx=10,pady=10,expand=True,fill=BOTH)
  input3=Entry(eqGroup,width=10)
  input3.pack()
  
  a=input1.get()
  b=input2.get()
  c=input3.get()
  
  a=DoubleVar() #Here I tried to re-type them all to a Float value, but it didn't work apparently
  b=DoubleVar()
  c=DoubleVar()
  
  temp1=pow(b/2,2) #I tried to do it in steps
  temp1=DoubleVar() #And to have the value conversion both before and after the assignment
  
  temp2=sqrt(temp1-c) #But no cookies for me :/
  temp2=DoubleVar()
  
  X1=(-b/2)+temp1 #I tried to convert 
  X2=(-b/2)-(sqrt(pow(b/2,2)-c)) #This is the PQ formula straight up, which does not work either
  </code></pre>
  
  <p>Pasteboard link to the entire thing: <a href="http://pastebin.com/Y77fHwmk" rel="nofollow noreferrer">http://pastebin.com/Y77fHwmk</a></p>
  
  <p>(the text is in Swedish there, because I'm from Sweden. But it's only in a few places, and it won't be relevant to the problem anyways)</p>
  
  <p>Please let me know if you have any ideas^^ I have not managed to fix this in way too long now. Headaches everywhere :/</p>
  
  <p>Traceback is here:</p>
  
  <p><a href="https://i.stack.imgur.com/8wobT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8wobT.png" alt="Traceback is here"></a></p>
  
  <p>Thanks guys :)</p>