title: Why is Button parameter "command" executed when declared?
body: <p>I'm new to Python and trying to write a program with tkinter.
  Why is the Hello-function below executed? As I understand it, the callback would only be executed when the button is pressed? I am very confused...</p>
  
  <pre><code>&gt;&gt;&gt; def Hello():
          print("Hi there!")
  
  &gt;&gt;&gt; hi=Button(frame,text="Hello",command=Hello())
  Hi there!
  &gt;&gt;&gt; 
  </code></pre>