PageRank in Python: maximum recursion depth exceeded

Question

I have a dataset - around 30000 users and I want to calculate an influence of each user based on UserRank algorithm, which is based on PageRank:

For each user I have a list of followers. I tried to calculate it in Python, but I'm getting:

RecursionError: maximum recursion depth exceeded while calling a Python object

Here's the code:

def calculate_user_rank(user_id):
    user_rank = 0
    for j in user[user_id]["followers"]:
        user_rank += (1 + (user[user_id]["followers_count"]/user[user_id]["tweets"]) * calculate_user_rank(j))/user[j]["followers_count"]
    return user_rank

Is there any way how to calculate this measure for each user?

can u try an iterative solution – Nitheesh MN Apr 28 '20 at 09:49 — Nitheesh MN, Apr 28 '20 at 09:49
What have you tried? Can you show your code? – Shubham Sharma Apr 28 '20 at 10:04 — Shubham Sharma, Apr 28 '20 at 10:04
@ShubhamSharma the code is above – Yakimget Apr 28 '20 at 10:13 — Yakimget, Apr 28 '20 at 10:13

score 0 · Answer 1 · answered Apr 28 '20 at 10:21

0

One way to deal with the problem is to utilise the concepts of dynamic programming, because you might be repetitively solving same sub-problem over and over. So, its better to store the result of the page ranks of user rather than calculating them again and again.

Use:

def calculate_user_rank(user_id, memo={}):
    user_rank = 0
    for j in user[user_id]["followers"]:
        if j not in memo:
            memo[j] = calculate_user_rank(j, memo)

        user_rank += (1 + (user[user_id]["followers_count"]/user[user_id]["tweets"]) * memo[j])/user[j]["followers_count"]
    memo[user_id] = user_rank

    return memo[user_id]

answered Apr 28 '20 at 10:21

Shubham Sharma

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@Yakimget What's the problem? – Shubham Sharma Apr 28 '20 at 11:28
"RecursionError: maximum recursion depth exceeded" again. I've sent you an email with user dictionary attached, so you can check your solution – Yakimget Apr 28 '20 at 11:54
@Yakimget didn't receive the mail. – Shubham Sharma Apr 28 '20 at 12:51
@Yakimget Got your mail, i have inspected it, and found out that there are follower id's for a particular user for which the corresponding user doesn't exists for e.g if `user_id = 11` then there is no user with `followerid = 9` – Shubham Sharma Apr 29 '20 at 04:40
I fixed it, but again I'm getting RecursionError – Yakimget May 05 '20 at 11:17

score 0 · Answer 2 · answered Apr 28 '20 at 10:22

You can always change the default recursion limit: What is the maximum recursion depth in Python, and how to increase it? But in this example I would prefer iterative solution for your problem (like here: https://github.com/thomasjhuang/PageRank/blob/master/run_pagerank.py) and cache for each user his score for performance.

PageRank in Python: maximum recursion depth exceeded

2 Answers2