我得到 TypeError: 'NoneType' object is not iterable, 当试图过滤列表时

Question

我试图通过取出所有类型为 None 的条目来过滤 Python 中的列表，但是当我尝试这样做时，我收到错误“TypeError: 'NoneType' object is not iterable”。我看不出哪里出错了。

原来的错误实际上是与该行一起出现的 如果 u"Restaurants" 不营业[u"categories"]： 我遇到与之前相同的错误，所以我尝试过滤几行以避免它，但我遇到了同样的问题

这是完整的代码块，尽管错误消息来自过滤器函数

import json

restaurant_ids = set()

# open the businesses file
with codecs.open(businesses_filepath, encoding='utf_8') as f:

    # iterate through each line (json record) in the file
    for business_json in f:
        # convert the json record to a Python dict
        business = json.loads(business_json)

        business[u"categories"] = filter(lambda a: a is not None, business[u"categories"])
        print business[u"categories"]

#         if this business is not a restaurant, skip to the next one
        if u"Restaurants" not in business[u"categories"]:
            continue

        # add the restaurant business id to our restaurant_ids set
        restaurant_ids.add(business[u'business_id'])

# turn restaurant_ids into a frozenset, as we don't need to change it anymore
restaurant_ids = frozenset(restaurant_ids)

# print the number of unique restaurant ids in the dataset
print '{:,}'.format(len(restaurant_ids)), u'restaurants in the dataset.'

我要过滤的文件由一个 JSON 组成，其中包含许多看起来像这样的条目。有些类别只是在其中包含“无”，这似乎是问题所在。

{"business_id":"1SWheh84yJXfytovILXOAQ","name":"Arizona Biltmore Golf Club","address":"2818 E Camino Acequia Drive","city":"Phoenix","state":"AZ" ,"postal_code":"85016","latitude":33.5221425,"longitude":-112.0184807,"stars":3.0,"review_count":5,"is_open":0,"attributes":{"GoodForKids":" False"},"categories":"Golf, Active Life","hours":null}

代码应该在 if 语句之后删除所有非“餐厅”类别，但我似乎无法达到那个阶段。

它会抛出错误

TypeError                                 Traceback (most recent call last)
<ipython-input-84-ac1362de4f26> in <module>()
     11         business = json.loads(business_json)
     12 
---> 13         business[u"categories"] = filter(lambda a: a is not None, business[u"categories"])
     14 #         print business[u"categories"]
     15 

TypeError: 'NoneType' object is not iterable

Answer 1

这个：

filter(lambda a: a is not None, business[u"categories"])

尝试从business["categories"] 中删除所有出现的None - 它假定business["categories"] 是可迭代的。如果是None（只有一个None，而不是包含None 的列表），它确实会引发这个确切的错误：

business = {"categories": None}
filter(lambda a: a is not None, business[u"categories"])

你要在这里测试business[u"categories"]是否是None，而不是它是否包含None。

使用 codecs.open(businesses_filepath, encoding='utf_8') as f:

# iterate through each line (json record) in the file
for business_json in f:
    business = json.loads(business_json)

    categories =   business[u"categories"]
    if categories is None:
        # if it's None it cannot contain "Restaurant" obviously
        continue

    if u"Restaurants" not in categories:
        continue

    # ok it's a restaurant