Build graph from log system

"""
now we have data with 3 properties
user_id, timestamp, action
100, 1000, A. 留学申请论坛-⼀亩三分地
200, 1003, A
300, 1009, B
100, 1026, B
100, 1030, C. 1point3acres
200, 1109, B
200, 1503, A
We want to output a graph to visualize it
Graph from input:
|---A (2)
| |---B (2)
| | |---C (1)
| | |---A (1)
|---B (1)
aggregate by user_id:
100 : A->B->C
200: A->B->A
300: B
"""

def build_log_system(logs):
    user_id, time_stamp, action = zip(*logs)
    user_id = sorted(list(set(user_id)))

    # construct a trie
    root = {'#': '#'}
    for uid in user_id:
        t = root
        for log in logs:
            if log[0] == uid:
                if log[2] not in t:
                    t[log[2]] = {'counter': 1}
                else:
                    t[log[2]]['counter'] += 1
                t = t[log[2]]
        t['#'] = '#'

    # traversal
    def dfs(node, level_so_far=''):
        if node == '#':
            return
        for next_action in node:
            if next_action not in ['counter', '#']:
                print('{}|---{}({})'.format(level_so_far, next_action, node[next_action]['counter']))
                dfs(node[next_action], level_so_far + '|\t')

    dfs(root)