title: Python gui button (tkinter) function is being run when program is executed and not onclick
body: <p>i'm currently learning python/tkinter and I have two buttons working correctly but my final button is assigned to a function, which is supposed to run on click but it instead runs when the program is executed and then will not run when the button is clicked. I have looked at a couple of other threads and cannot work out why mine wont work.</p>
  
  <p>Thanks a lot</p>
  
  <pre><code>def onclickSelectSheet(): 
      test()
  
  buttonSelectSheet = Button(topFrame, text="Select an information sheet", command=onclickSelectSheet(), bg = '#CDCDCD')
  buttonSelectSheet.place(relx=0.2, rely=0.1, relwidth=0.6, relheight=0.4) 
  </code></pre>