title: Python If/else statements with math
body: <p>I've been trying to make a circle area calculator, and I've got the basics. But if the user enters something like <code>5m</code>, then I see an error. Instead of exiting with an error, I want to return "Enter a Number". Here is my code.</p>
  
  <pre><code>from math import pi
  
  r = float(input("Input the radius of the circle : "))
  print("The area of the circle with radius " + str(r) + " is: " + str(pi * r**2))
  
  if r==(str):
      print("Enter a Number")
  </code></pre>