title: how to ask for user input in a function. Python related
body: <p>Is there a way to ask for user input while defining a function?
  for example here's a simple function:</p>
  
  <pre><code>def sum3(a,b,c):
      add=a+b+c
      return add
  </code></pre>
  
  <p>in the above code, is there a way I can ask the user to
  enter 3 numbers.
  say, when the program runs
  the user sees a prompt saying "please enter 3 numbers"</p>