Debugging in Python, part 5: Working through multiple bugs

MP 144: What happens when you fix a bug, only to find another bug right away?

Note: This post is part of an ongoing series about debugging in Python. The posts in this series will only be available to paid subscribers for the first 6 weeks. After that they will be available to everyone. Thank you to everyone who supports my ongoing work on Mostly Python.

We often think of debugging as fixing a bug, when in reality there's usually a number of bugs we have to work through before things start working again. In the previous examples in this series, fixing one bug brought the project to a working state again. In this post, we'll see what happens when fixing one bug leaves you with a project that's still broken.

Fixing a bug

We'll stick with the Dice Battle example one more time. I've introduced more than one bug in the project; here's what happens when we run it now:

$ python dice_battle.py 
  File "dice_battle.py", line 18
    for _ in range(num_battles):
IndentationError: unexpected indent

There's an IndentationError in the main file. Let's take a look at that section of code:

...
# Simulate some battles between players A and B.
num_battles = 10
results = {...}

    for _ in range(num_battles):
    a_result, b_result = utils.battle()
    print(f"\nPlayer A: {a_result}")
    print(f"Player B: {b_result}")
...

Here, the for statement is indented along with the body of the loop. Let's unindent the first line of the loop:

...
# Simulate some battles between players A and B.
num_battles = 10
results = {...}

for _ in range(num_battles):
    a_result, b_result = utils.battle()
...

That should fix the issue. Let's try running the program again:

$ python dice_battle.py 
Traceback (most recent call last):
  File "dice_battle.py", line 7, in <module>
    import utils
  File "utils.py", line 3, in <module>
    from die import Die
  File "die.py", line 1, in <module>
    import randaom
ModuleNotFoundError: No module named 'randaom'

Oh no, now there's an even longer traceback! Did we mess something up?