AttributeError：“dict”对象没有属性“predictors”

Question

我是 python 新手，找不到答案。参考消息末尾的代码，我能知道下面一行中的“for item, total in totals.items()”部分是什么意思吗？

 rankings = [(total/simSums[item], item) for item, total in totals.items()]

此外，代码失败并说

AttributeError：“dict”对象没有属性“predictors”

当我将代码中“项目”的所有实例更改为“预测器”时。为什么呢？

 # Return the Pearson correlation coefficient for p1 and p2
def sim_person(prefs, p1, p2):
    # Get the list of shared_items
    si={}
    for item in prefs[p1]:
        if item in prefs[p2]:si[item]=1

    # Find the number of elements
    n=len(si)

    # if they have no ratings in common, return 0
    if n==0: return 0

    # Add up all the preferences
    sum1 = sum([prefs[p1][it] for it in si])
    sum2 = sum([prefs[p2][it] for it in si])

    # Sum up the squares
    sum1Sq = sum([pow(prefs[p1][it],2) for it in si])
    sum2Sq = sum([pow(prefs[p2][it],2) for it in si])

    # Sum up the products
    pSum = sum([prefs[p1][it]*prefs[p2][it] for it in si])

    # Calculate Person score
    num = pSum - (sum1*sum2/n)
    den = sqrt((sum1Sq - pow(sum1,2)/n)*(sum2Sq - pow(sum2,2)/n))
    if den == 0: return 0

    r = num/den
    return r

# Returns the best matches for person from the prefs dictionary.
# Number of results and similarity function are optional params.
def topMatch(prefs, person, n=5, similarity=sim_person):
    scores = [(similarity(prefs, person, other), other)
              for other in prefs if other!=person]

    # Sort the list so the highest scores appear at the top
    scores.sort()
    scores.reverse()
    return scores[0:n]

# Gets recommendations for a person by using a weighted average
# of every other user's rankings
def getRecommendations(prefs, person, similarity=sim_person):
    totals = {}
    simSums = {}
    for other in prefs:
        # don't compare me to myself
        if other == person: continue
        sim = similarity(prefs, person, other)

        # ignore scores of zero of lower
        if sim<=0: continue
        for item in prefs[other]:

            # only score movies I haven't seen yet
            if item not in prefs[person] or prefs[person][item]==0:
                # Similarity * Score
                totals.setdefault(item, 0)
                totals[item]+=prefs[other][item]*sim
                # Sum of similarities
                simSums.setdefault(item, 0)
                simSums[item]+=sim

    # Create the normalized list
    rankings = [(total/simSums[item], item) for item, total in totals.items()]

    # Return the sorted list
    rankings.sort()
    rankings.reverse()
    return rankings

原文由 Mike 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

dict.items 迭代字典的键值对。因此 for key, value in dictionary.items() 将遍历每一对。这是文档化的信息，您可以在 官方网页 中查看，或者更简单，打开 python 控制台并输入 help(dict.items) 。现在，举个例子：

 >>> d = {'hello': 34, 'world': 2999}
>>> for key, value in d.items():
...   print key, value
...
world 2999
hello 34

AttributeError 是当对象不具有您尝试访问的属性时引发的异常。类 dict 没有任何 predictors 属性（现在您知道在哪里检查它:)），因此当您尝试访问它时它会抱怨。就这么简单。

原文由 bgusach 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 2

尝试没有像这样的点符号：

 sample_dict = {'name': 'John', 'age': 29}
print(sample_dict['name']) # John
print(sample_dict['age'])  # 29

原文由 Shirantha Madusanka 发布，翻译遵循 CC BY-SA 4.0 许可协议