Question

我是python的新手，无法找到答案。参考消息末尾的代码，我是否可以知道该部分＆＃34;对于item，total in totals.items（）＆＃34;在下面的行中意味着什么？

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

此外，代码失败并说

属性错误：＆＃39; dict＆＃39;对象没有属性＆＃39;预测者＆＃39;

当我更改＆＃34; item（s）＆＃34;的所有实例时在代码中＆＃34;预测者＆＃34;。为什么会这样？

# 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

Answer 1

dict.items遍历字典的键值对。因此for key, value in dictionary.items()会遍历每一对。这是记录在案的信息，您可以在official web page中查看，甚至更容易，打开一个python控制台并输入help(dict.items)。现在，仅作为一个例子：

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

当对象没有您尝试访问的属性时，AttributeError是抛出的异常。类dict没有任何predictors属性（现在你知道在哪里检查:)），因此当你尝试访问它时会抱怨。就这么简单。

Answer 2

#Try without dot notation
sample_dict = {'name': 'John', 'age': 29}
print(sample_dict['name']) # John
print(sample_dict['age']) # 29

Answer 3

product_details = {
'name':'mobile',
'company':'samsung'}

访问 product_details.name 会抛出错误“dict object has no attribute 'name'”。原因是因为我们使用点 (.) 来访问字典项。

right way is :
product_details['name']

我们使用点运算符从 Python 中的对象访问值。

dictionary.items() 允许我们遍历字典中的键值对

for key, value in product_details.items(): 
    print(key,':',value)

对于循环的每次迭代，一个键和它的值被分配给这里的变量键和值。这就是 items() 方法的工作原理。

AttributeError：＆＃39; dict＆＃39;对象没有属性＆＃39;预测者＆＃39;

3 个答案: