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Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today. # Can someone explain to me in detail about how this script is running?

travel_expenses = [ [5.00, 2.75, 22.00, 0.00, 0.00], [24.75, 5.50, 15.00, 22.00, 8.00], [2.75, 5.50, 0.00, 29.00, 5.00], ] print("Travel Expenses") week_number = 1 for week in travel_expenses: print("* Week #{}: \${}".format(week_number, sum(week))) week_number += 1

i have a basic understanding about what is going on, but i feel like i need a bit more clarity with multi dimensional lists. i understand how rows and columns work in this list, but how about the lines of code under it?

I appreciate a response in advance!!

```# travel_expenses is a list of lists.  each sublist presumably contains the expenses for each
# day of a week as there are five values.
travel_expenses = [ [5.00, 2.75, 22.00, 0.00, 0.00], [24.75, 5.50, 15.00, 22.00, 8.00], [2.75, 5.50, 0.00, 29.00, 5.00], ]
print("Travel Expenses")
# initialize the week_number variable to track the iteration through the list of weeks (sublists).
week_number = 1
# the for loop will iterate through each item (i.e., sublist) in the list of weeks (travel_expenses)
for week in travel_expenses:
# for each "week" or sublist in travel_expenses, print a label indicating the "Week #" followed
# by the sum or total of the five days of expenses for that week.  Note:  the curly brackets "{}"
# are placeholders for the values contained in the variables/expressions:  "week_number" and
# "sum(week)."  "week_number" starts at 1 and then before the next week sublist is iterated,
# "week_number" gets incremented by 1 with the statement "week_number += 1.  "sum(week)" evaluates
# to the sum or total of the five daily expense values in each week (Note:  the for loop uses the
# variable "week" to iterate through travel_expenses, so each time through the loop, "week" is
# equal to one of the sublists contained in travel expenses.
print("* Week #{}: \${}".format(week_number, sum(week)))
week_number += 1
```

I apologize if this explanation is too verbose! As a final observation, I prefer to use "enumerate" to iterate through lists when I need to access the index of the item (in this case to extract the number of the week). The code below shows this implementation which simplifies things a little:

```travel_expenses = [ [5.00, 2.75, 22.00, 0.00, 0.00], [24.75, 5.50, 15.00, 22.00, 8.00], [2.75, 5.50, 0.00, 29.00, 5.00], ]
print("Travel Expenses")
for index, week in enumerate(travel_expenses):
print("* Week #{}: \${}".format(index + 1, sum(week)))
```

Note: since indexing in Python starts at 0, (i.e., the first week of data can be accessed with: travel_expenses), we need to offset the index variable by 1