More progress bars for slow loops, and refactor

[hugovk]

Also in Python we generally prefer to iterate over objects in a list (or tuple, or other so-called "iterable") rather than using an index of range(len(thing)).

So for example, instead of:

n = len(activities)
for i in range(n):
    print(activities[i])

This is more direct and readable:

for activity in activities:
    print(activity)

If we do need an index as well, enumerate is often used:

for i, activity in enumerate(activities):
    print(i, activity)

[marcusvolz]

Noted, many thanks Hugo!