Question

Possible Duplicate:
Function printing correct Output and None

Trying to print mutual users in a pretend twitter feed program. Homework. The numbers are users (ex 1111 is a user). The following set in the dictionary is a set of the key’s friends.

I’d like this output:

Most friends in common
1111:   222 33333 5454
222:    1111 33333 5454
33333:  1111 222
5454:   1111 222

But instead have this output:

Most friends in common
1111 :  222 33333 5454  1111 None
222 :   1111 33333 5454  222 None
33333 :  1111 222  33333 None
5454 :   1111 222  5454 None

Here is my program:

all_users = {'1111': set(['5454', '222']), '33333': set(['5454']), '5454': set(['1111', '33333', '222']), '222': set(['1111', '5454'])}



def findmutual(id, all_users):
    users = []
    for key in all_users:
        mutual = all_users[id].intersection(all_users[key])
        rank = len(mutual)
        templist = [rank, key.strip()]
        users.append(templist)
    users = sorted(users)

    print users

    for item in users:
        if  id == item[1]:
            print "" ,
        if item[0] == 0:
            print "",
        else:
            print item[1],


users = []
for key in all_users:
    users.append(key)
users = sorted(users)
print "Most friends in common"
for item in users:
    print item, ":\t", findmutual(item, all_users)

Please help me to understand this issue!

Answer 1

for item in users:
    print item, ":\t", findmutual(item, all_users) # << That's why it shows None

What is happening here?

1. item = users[n]
2. print:
   1. item
   2. enter the function
   3. the function prints some more
   4. function ends and (automatically) returns None
   5. print the return value (which is None) of the function!

You probably want to change step 3-4!
instead of all print statements smth like:

result=''
...
result += '' #whatever
...
return result

UPDATE:

If i get you right, you are trying to establish a rank depending on who’s the most popular?

In that case you might look int othat solution:

all_users = {'1111': set(['5454', '222']),
             '33333': set(['5454']),
             '5454': set(['1111', '33333', '222']),
             '222': set(['1111', '5454'])}

from collections import defaultdict, Counter

def findmutual(user_relation_map):    
    user_list = set(sorted(user_relation_map.keys()))
    user_ranking = defaultdict(int)
    for user in user_list:
        for friend in user_relation_map[user]:
            user_ranking[friend] += 1
    return user_ranking

c=Counter(findmutual(all_users))
print("Ranking : {0}".format(c.most_common()))

>>> Ranking : [('5454', 3), ('1111', 2), ('222', 2), ('33333', 1)]