Debugging Like a Pro (Even When You Are 10)

Every professional programmer writes broken code every single day. The difference is that they have a routine for fixing it.

The four-step routine

• Read the error message out loud. It usually names the line.
• Print the values around that line to see what the computer sees.
• Change one thing at a time, then run it again.
• Explain the problem to a pet, a plant or a rubber duck.

Printing your way out of trouble

 1total = 0
 2prices = [3, 5, "7"]
 3
 4for price in prices:
 5    print("adding", price, type(price))  # the clue is here
 6    total += int(price)
 7
 8print("Total:", total)