通过简单的Social Network程序，练习到目前为止的编程概念，如2D list和functions, 以及学习异常处理相关try/except的语法，防止程序崩溃。
The goal of this assignment is to learn and practice the concepts covered thus far. In particular you will get more practice with (2D) lists and functions. For one of the functions you will also need to learn how to prevent syntax errors i.e. crashes by learning about try/except concept for handling exceptions. Given the goals of this assignment, you cannot user: dictionaries, sets, deque, bisect module. You can though, and in fact should, use .sort or sorted functions.
As always, you can make multiple submissions, but only the last submission before the deadline will be graded.
For this assignment, you only need to submit one file, called a4_xxxxxx.py, where you changed xxxxxx to your student number. (No need to submit a4_xxxxxx.txt as proof that you tested your function. By now we trust that you learnt and understand the need and importance for testing your functions and code in general).
For this assignment, I provided you with starter code in file called a4_xxxxxx.py. Begin by replacing xxxxxx in the file name with your student number. Then open the file. Your solution (code) for the assignment must go into that file in the clearly indicated spaces. The file has main completely coded for you. Nothing else will go into the mail. It also has some functions completely precoded for you. Your task will me to code the remaining functions. You are not allowed to delete or comment-out any parts of the provided code. The only exception to that rule is the keyword pass. Some functions have that keyword. You can remove it once you are done coding that function. You also must follow the instructions given in comments and implied by docstrings. You are however allowed to add your own additional (helper) functions. In, fact you should add at least one more function.
I have provided 5 text files to test and debug your code with as explained in the next section.
As always, your program must run without syntax errors. In particular, when grading your assignment, TAs will first open your file a4_xxxxxx.py with IDLE and press Run Module. If pressing Run Module causes any syntax error, the grade for the assignment becomes zero. Furthermore, for each function whose code is missing, I have provided below one or more tests to test your functions with. To obtain a partial mark for these function your solutions may not necessarily give the correct answer on these tests. But if your function gives any kind of Python error when run on the tests provided, that function will be marked with zero points. Finally, each function has to be documented with docstrings.
There is also a4-more-example-runs.txt file, giving additional example runs to those given in the next section. The behaviour of all example runs below and in a4-more-example-runs.txt should be considered as an implied requirement for the assignment - as always.
Using global variables inside of functions is not allowed. If you do not know what that means, for now, interpret this to mean that inside of your functions you can only use variables that are created in that function. For example, the following code fragment would not be allowed, since variable x is not a parameter of function a_times(a) nor is it a variable created in function a_times(a). It is a global variable created outside of all functions.
x=float(input("Give me a number: "))
Have you ever wondered how social networks, such as Facebook, recommend friends to you? Most of the social networks use highly sophisticated algorithms for this, but for this assignment you will implement a fairly naive algorithm to recommend the most likely new friend to users of a social network. In particular, you will recommend the most probable user to befriend based upon the intersection of your common friends. In other words, the user that you will suggest to Person A is the person who has the most friends in common with Person A, but who currently is not friends with Person A.
Five text files have been provided for you to run your program with. Each represents a social network. Three are small test files containing a made-up set of users and their friendships (these files are net1.txt, net2.txt and net3.txt). The two are a subset of a real Facebook dataset, which was obtained from: fhttps://snap.stanford.edu/data/egonets-Facebook.html
The format of all five files is the same:
The first line of the file is an integer representing the number of users in the given network.
The following lines are of the form: user_u user_v where user_u and user_v are the (non-negative integer) IDs of two users who are friends.
In addition user_u is always less than user_v
For example, here is a very small file that has 5 users in the social network: 5
01 12 18 23
The above is a representation of a social network that contains 5 users.
User ID=0 is friends with User IDs = 1 User ID=1 is friends with User IDs = 0, 2, 8 User ID=2 is friends with User IDs = 1, 3 User ID=3 is friends with User IDs = 2 User ID=8 is friends with User IDs = 1
Spend time studying the above small example to understand the model. For example, notice that since friendship is a symmetric relationship the social media networks in this assignment, if user_u is friends with user_v, that means that user_v is also friends with user_u. Such “duplicate” friendships are not present in the file. In particular each friendship is listed once in such way that
user_u < user_v
Also note that, while you can assume that user IDs are sorted, you cannot assume that they are consecutive integers differing by one. For example the user IDs above are: 0,1,2,3,8.
You can also assume that in each file the users are sorted from smallest to largest (in the above example you see that users appear as: 0 1 1 2). Specifically, friendships of user_u appear before friendships of user_v if and only if
user_u < user_v. And also for each user its friends appear sorted, for example for user 1 friendship with friend 2 appears before friendship with friend 4.
To complete the assignment you will have to code the following 9 functions. I strongly recommend you code the in the order given below and do not move onto coding a function until you complete all before. The function descriptions, including what they need to do, are given in a4_xxxxxx.py.
This is the most important (and possibly the most difficult) function to solve. The function needs to read a file and return a list of tuples representing the social network from the file. In particular the function returns a list of tuples where each tuple has 2 elements: the first is an integer representing an ID of a user and the second is the list of integers representing his/her friends. In the a4_xxxxxx.py I refer the list that create_network function returns as a 2D-list for friendship network (although one can argue that is is a 3D list). In addition the 2D-list for friendship network that must create_network function returns must be sorted by the ID and a list of friends in each tuple also must be sorted.
So for the example above, this function should return the following 2D-list for 2D-list for friendship network:
[(0, ), (1, [0,2,8]), (2,[1,3]), (3,), (8,)]
>>> net1=create_network("net1.txt") >>> net1 [(0, [1, 2, 3]), (1, [0, 4, 6, 7, 9]), (2, [0, 3, 6, 8, 9]), (3, [0, 2, 8, 9]), (4, [1, 6, 7, 8]), (5, ), (6, [1, 2, 4, 8]), (7, [1, 4, 8]), (8, [2, 3, 4, 6, 7]), (9, [1, 2, 3, 5])] >>> net2=create_network("net2.txt") >>> net2 [(0, [1, 2, 3, 4, 5, 6, 7, 8, 9]), (1, [0, 4, 6, 7, 9]), (2, [0, 3, 6,8, 9]), (3, [0, 2, 8, 9]), (4, [0, 1, 6, 7, 8]), (5,[0,9]),(6,[0,1,2,4,8]), (7,[0,1,4,8]),(8,[0,2,3,4,6,7]),(9,[0,1,2,3,5])] >>> net3=create_network("net3.txt") [(0, [1, 2, 3, 4, 5, 6, 7, 8, 9]), (1, [0, 4, 6, 7, 9]), (2, [0, 3, 6,8, 9]), (3, [0, 2, 8, 9]), (4, [0, 1, 6, 7, 8]), (5, [0, 9]), (6, [0, 1, 2, 4, 8]), (7, [0, 1, 4, 8]), (8, [0, 2, 3, 4, 6, 7]), (9, [0, 1, 2, 3, 5]), (100, ), (112, [100, 114]), (114, )] >>> net4=create_network("big.txt") >>> net4[500:502] [(500, [348, 353, 354, 355, 361, 363, 368, 373, 374, 376, 378, 382, 388, 391, 392, 396, 400, 402, 404, 408, 409, 410, 4
>>> getCommonFriends(3,1,net1) [0, 9] >>> getCommonFriends(0,112,net3)  >>> getCommonFriends(217,163,net4) [0, 100, 119, 150]
Read the docstrings to understand how this function should work. Understand why the given friends are recommended in the examples below including why no friend is recommended for 0 in net2 and 112 in net 3.
>>> recommend(6,net1) 7 >>> recommend(4,net2) 2 >>> recommend(0,net2) >>> recommend(114, net3) 100 >>> recommend(112,net3) >>> recommend(217,net4) 163
>>> k_or_more_friends(net1, 5) 3 >>> k_or_more_friends(net2, 8) 1 >>> k_or_more_friends(net3, 12) 0 >>> k_or_more_friends(net4, 70) 33
>>> maximum_num_friends(net1) 5 >>> maximum_num_friends(net2) 9 >>> maximum_num_friends(net3) 9 >>> maximum_num_friends(net4) 347
>>> people_with_most_friends(net1) [1, 2, 8] >>> people_with_most_friends(net2)  >>> people_with_most_friends(net3)  >>> people_with_most_friends(net4) 
>>> average_num_friends(net1) 3.8 >>> average_num_friends(net2) 5.0 >>> average_num_friends(net3) 4.153846153846154 >>> average_num_friends(net4) 19.78
>>> knows_everyone(net1) False >>> knows_everyone(net2) True >>> knows_everyone(net3) False >>> knows_everyone(net4) False
>>> get_uid(net1) Enter an integer for a user ID:alsj That was not an integer. Please try again. Enter an integer for a user ID:twenty That was not an integer. Please try again. Enter an integer for a user ID:9aslj That was not an integer. Please try again. Enter an integer for a user ID:100000 That user ID does not exist. Try again. Enter an integer for a user ID:4.5 That was not an integer. Please try again. Enter an integer for a user ID: -10 That user ID does not exist. Try again. Enter an integer for a user ID:-1 That user ID does not exist. Try again. Enter an integer for a user ID:7
This assignment offers up to 15% bonus. The bonus is available for the maximum of 30-40 students. In order for a student to have a chance to get the bonus the following needs to happen:
She needs to correctly solve/code create_network and getCommonFriends functions. She will know that that is the case by waiting for the grading to be completed and seeing that she did not loose any points on these 2 functions; and
She needs to solve getCommonFriends(user1, user2, network) with running time
O(n1 + n2 + log n) were n is the the total number of users in the network, n1 is the number of friends of user1 and n2 is the number of friends of user2. In other words, n1 =len(user1), n2 =len(user2) and n =len(network).
Note that on a typical network O(n1 +n2 +log n) is much better than O(n) since a network like Facebook has n roughly 2 billion and the average number of friends per user is 338. Thus the number of operations an O(n) solution would do, would be in the order of a billion, roughly. While the number of operations an O(num_friends_user1 + num_friends_user2 + log n) solution would do, would be in the order of, O(338 + 338 + 21), thousand, roughly
Thus O(n) solutions will not be accepted for the bonus.
To determine the running times of Python’s functions on lists you can use this link (although it is not quite correct as it is amortized, which they incorrectly call average, analysis and not the worst case analysis). https://wiki.python.org/moin/TimeComplexity
Again you cannot use sets nor dictionaries nor deque nor bisect module.