Iterating over a list
Modifying lists
Working with multiple lists
Congratulations
Instruction
That's right! We can also modify a list by deleting some of its elements.
Deleting elements while iterating over a list is a bit tricky. Let's assume we have some erroneous values in our sleep_durations list (e.g., negative values) and we want to get rid of them. We may be tempted to write the following code:
# not gonna work!
sleep_durations = [268, -590, -326, 506]
for duration in sleep_durations:
if duration < 0:
sleep_durations.remove(duration)
print(sleep_durations)
What's wrong with this code? Let's find out!
Exercise
Run the template, which contains the code from the explanation.
As you can see, the code removed -590 from the list, but kept the value of -326. Why is that so?
The problem is that we iterate over the list and not over the indexes. Take a look at the diagram:
