title: How do i import these functions? Attribute Error
body: <p>I just began studying python and created a simple calculator GUI with python and tkinter. The Buttons work but for some reason when i try to move the functions to another file and import them it doesnt work and i get an AttributeError.</p>
  
  <p>Mainfile:</p>
  
  <pre><code>from tkinter import *
  from functions_calc_advanced import *
  
  if _name_ == "_main_":
  
      gui = Tk()
      gui.configure(background="white")
      gui.title("LABINF Calculator WSS2018")
      gui.geometry("400x200")
  
      equation = StringVar()
  
      expression_field = Entry(gui, textvariable=equation)
      expression_field.grid(columnspan=4, ipadx=10)
      equation.set('enter your expression')
  </code></pre>
  
  <p>The window opens but when i press any button i get an error. This button1 is just an example all the other buttons are structured the same way</p>
  
  <pre><code>    button1 = Button(gui, text=' 1 ',command=lambda: press(1), height=1, width=7)
      button1.grid(row=4, column=0)
  
      buttonauf = Button(gui, text=' ( ', fg='black', bg='grey',command=lambda: press('('), height=1, width=7)
      buttonauf.grid(row=5, column=0)
  
      buttonzu = Button(gui, text=' ) ', fg='black', bg='grey',command=lambda: press(')'), height=1, width=7)
      buttonzu.grid(row=6, column=0)
  
      buttondot = Button(gui, text=' . ', fg='black', bg='grey',command=lambda: press('.'), height=1, width=7)
      buttondot.grid(row=5, column=2)
  
      buttonquit = Button(gui, text="Quit", command = gui.destroy, bg = 'black', fg = "white")
      buttonquit.grid(row = 0, column = 4)
  </code></pre>
  
  <p>Calculation Buttons</p>
  
  <pre><code>    plus = Button(gui, text=' + ', fg='orange', bg='white', command=lambda: press("+"), height=1, width=2)
      plus.grid(row=2, column=3)
  
      minus = Button(gui, text=' - ', fg='orange', bg='white', command=lambda: press("-"), height=1, width=2)
      minus.grid(row=3, column=3)
  
      mult = Button(gui, text=' * ', fg='orange', bg='white', command=lambda: press("*"), height=1, width=2)
      mult.grid(row=4, column=3)
  
      div = Button(gui, text=' / ', fg='orange', bg='white', command=lambda: press("/"), height=1, width=2)
      div.grid(row=5, column=3)
  
      equal = Button(gui, text=' = ', fg='white', bg='orange', command=equalpress, height=1, width=7)
      equal.grid(row=6, column=3)
  
      clear = Button(gui, text='C', fg='white', bg='black', command=clear, height=1, width=7)
      clear.grid(row=0, column=3)
  
      gui.mainloop()
  </code></pre>
  
  <p>Functions file i am trying to import from:</p>
  
  <pre><code>expression = ""
  equation = ""
  def press(num):
      global expression
      expression = expression + str(num)
      equation.set(expression)
  
  def equalpress():
      try:
          global expression
          total = str(eval(expression))
          equation.set(total)
          expression = ""
  
      except: 
          equation.set(" error ")
          expression = ""
  
  def clear():
      global expression
      expression = ""
      equation.set("")
  </code></pre>