A queue should remove every completed task.
What You Need to Understand
Removing elements from a list while iterating over that same list can skip items because indexes shift. A filtered copy or slice assignment is often clearer and safer.
When to Use It
A queue should remove every completed task.
Step-by-Step Python Example
tasks = ["done", "done", "open", "done"]
tasks = [task for task in tasks if task != "done"]
print(tasks)How the Example Works
The new list contains only open, avoiding index changes during iteration.
Example Output
['open']
[1, 3]A Second Example
Compare this smaller variation with the main example, then experiment with your own values.
values = [1, 2, 3, 4]
values[:] = [value for value in values if value % 2]
print(values)Important Behavior and Edge Cases
If other code holds a reference to the original list, reassignment will not update it. Use tasks[:] = [...] when you must preserve the original object.
Try It Yourself
Remove every even number from a list while keeping the same list identity.
Common Beginner Mistakes
- If other code holds a reference to the original list, reassignment will not update it. Use
tasks[:] = [...]when you must preserve the original object. - Overlooking how an iterable is consumed, how element positions are chosen, or whether a function creates a new list.
Key Takeaways
- Removing elements from a list while iterating over that same list can skip items because indexes shift.
- The new list contains only
open, avoiding index changes during iteration. - If other code holds a reference to the original list, reassignment will not update it.