Python属性错误：numpy.ndarray没有属性项

Question

我的代码如下所示：

from copy import deepcopy
from csv import DictReader, DictWriter
from datetime import datetime
from collections import Counter
from numpy import array


with open('sessions.csv') as in_f:
    reader = DictReader(in_f)
    hits = {}
    session_lengths = {}
    for line in reader:
        identifier = '%s_%s' % (line['remote_host'], line['session'])
        timestamp = datetime.strptime(line['time_received_isoformat'], '%Y-%m-%dT%H:%M:%S')
        if identifier in hits:
            hits[identifier] = hits[identifier] + 1
        else:
            hits[identifier] = 1
        if identifier in session_lengths:
            session_lengths[identifier] = (session_lengths[identifier][0], timestamp)
        else:
            session_lengths[identifier] = (timestamp, timestamp)
    print(Counter(hits.values()))
    session_lengths = [(end - start).seconds for (start, end) in session_lengths.values()]
    session_lengths = array(session_lengths)
    print(session_lengths.max() / 60)
    print(session_lengths.mean() / 60)
    print(session_lengths.std() / 60)

    print(Counter(hits.values()))
    for key, (start, end) in session_lengths.items():
        if (end - start).seconds > 30000:
            print(key)

这是我的代码中显示错误的部分：

print(Counter(hits.values()))
for key, (start, end) in session_lengths.items():
    if (end - start).seconds > 30000:
        print(key)

错误： AttributeError：＆＃39; numpy.ndarray＆＃39;对象没有属性＆＃39;项目＆＃39;