code in python $.$ For the following, all functions must have a proper docstring and annotations. Use try$/$except and in

case of an error print a user$-$friendly message to the terminal and raise or re$-$raise the exception.

Write a simplified social network data structure using dictionaries, lists and tuples.

The social network is stored in a Python dictionary with information for each social network user

indexed by the username. A

user

is represented by a tuple with this format: $($full$\_$name, $[$friend$1,$

friend$2,....]),$ where each list element is a string and friend$1,$ friend$2$ are usernames of the current

user$$s $$friends$.$

An example of a social network showing usernames and the

friend

links is this:

alice $$ maria $$ joe $$ eve

$|$

david

This network can be represented by this dictionary:

$\{\text{'}$alice$\text{'}$: $(\text{'}$Alice Smith', $[\text{'}$maria$\text{'}]),$

'maria': $(\text{'}$Maria Cortez', $[\text{'}$alice$\text{'},$ 'joe', 'david'$]),$

'joe': $(\text{'}$Joseph Adams', $[\text{'}$maria$\text{'},$ 'eve'$]),$

'eve': $(\text{'}$Evelyn Cooper', $[\text{'}$joe$\text{'}]),$

'david': $(\text{'}$David Benson', $[\text{'}$maria$\text{'}])\}$

a$)$ Write a function

add$\_$user

$($sn$,$ username, fullname$)$ that adds to the social network stored in

dictionary sn a new user with the given username and full name. The new user has initially no friend

links. The function returns True if the user was added successfully and False, otherwise, i$.$e$.$ if the user

existed before.

b$)$ Write a function

add$\_$friend

$($sn$,$ user$1,$ user$2)$ that takes a dictionary sn with a social network and

adds a mutual friend link between users user$1$ and user$2.$ The function returns True if success, and

False otherwise, e$.$g$.$ when at least one the user names given are not found in sn$.$

c$)$ Write a function

get$\_$friends

$($sn$,$ user$1,$ distance$)$ that takes a dictionary sn with a social network, a

username in argument user$1,$ and a positive integer in argument distance and that returns a list with all

friends of user$1$ at link distance $1,2,...,$ distance.

Friends at distance$=1$ of a user are the users in its immediate list of friends:

get$\_$friends$($sn$,$alice$,1)$ returns $[$maria$]$

Friends at distance$=2$ of a user are the users at distance $1$ and the users in the immediate friend lists of

users at distance $1$:

get$\_$friends$($sn$,$alice$,2)$ returns $[$maria$,$joe$,$david$]$

The function returns the empty list if the are no friends to return or if the given user name is wrong.

Hint: you need to avoid cycles.

d$)$ Write a function

save$\_$network

$($filename$,$ sn$)$ that saves a social network dictionary to a $.$CSV file.

The function takes as parameter the file name and the dictionary.

Let your function throw relevant

exceptions, e$.$g$.$ FileNotFoundError.

e$)$ Write a function

load$\_$network

$($filename$)$ that reads a social network from a $.$CSV file saved with

save$\_$network$(...)$ and that returns the dictionary object. Let your function throw relevant exceptions.

f$)$ Write a

main

function that tests all the functions above.