Instructions

Write a function get$\_$list$\_$avg$()$ that expects a parameter main$\_$list $($a list of lists$)$ and returns a new list that contains the average of each sub$-$list in main$\_$list. The function should return an empty list if the main$\_$list is empty.

The example below guides you step$-$by$-$step through the process. If you understand what needs to happen and how to accomplish it$,$ then you can go directly to writing your function and testing it with the assert statements.

### Check that the computation is correct

assert get$\_$list$\_$avg$([[10,0,2],[5,10,6],[7,8,9]])==[4\mathrm{.}0,7\mathrm{.}0,8\mathrm{.}0]$

assert get$\_$list$\_$avg$([[10,0,2],[5,10,6],[7,8,9],[5,10,6]])==[4\mathrm{.}0,7\mathrm{.}0,8\mathrm{.}0,7\mathrm{.}0]$

assert get$\_$list$\_$avg$([[10,0,2,5,10,6],[7,8,9]])==[5\mathrm{.}5,8\mathrm{.}0]$

### Verify that the original list is unchanged

sample$\_$list $=[[10,0,2],[5,10,6],[7,8,9]]$

get$\_$list$\_$avg$($sample$\_$list$)$ # call the function on a sample list

assert sample$\_$list $==[[10,0,2],[5,10,6],[7,8,9]]$ # verify that sample list was unchanged

Walkthrough Example

Given a sample list $[[10,0,2],[5,10,6],[7,8,9]],$ it can be formatted as follows to show its structure $(3$ nested sub$-$lists$)$:

num$\_$list $=[$

$[$

$10,$

$0,$

$2$

$],$

$[$

$5,$

$10,$

$6$

$],$

$[$

$7,$

$8,$

$9$

$]$

$]$

Loop over the main list to retrieve each element of this list, which is also a list:

for sublist in num$\_$list:

print$($sublist$)$

and produce

$[10,0,2]$

$[5,10,6]$

$[7,8,9]$

Compute an average of each sub$-$list, which is the sum of that list divided by the number of elements in that list.

To assemble a new list that would hold the average values of each sub$-$list, we need to create an empty list outside of the loop and then append the computed average values at the end of each iteration.

list$\_$avg $=[]$

for sublist in num$\_$list:

$...$

list$\_$avg.append$($avg$)$

print$($list$\_$avg$)$

Now that you have each step, turn them into a proper function that returns the correct result.

Hints

Refer to the following zyBook resources to review how to work with nested lists:

PA $7\mathrm{.}5\mathrm{.}1$: List nesting.

PA $7\mathrm{.}5\mathrm{.}5$: Iterating over multi$-$dimensional lists.

zyDE $7\mathrm{.}3\mathrm{.}2$: Using built$-$in functions with lists.

zyDE $7\mathrm{.}5\mathrm{.}1$: Two$-$dimensional list example: Driving distance between cities.

Figure $7\mathrm{.}5\mathrm{.}4$: Iterating through multi$-$dimensional lists using enumerate$().$

Remember that you wrote calc$\_$average$()$ in the previous lab $-$ use it as a helper function here.