Question

我有一个json格式列表，每个列表中都有一些字典，它看起来像以下内容：

[{"id":13, "name":"Albert", "venue":{"id":123, "town":"Birmingham"}, "month":"February"},
{"id":17, "name":"Alfred", "venue":{"id":456, "town":"London"}, "month":"February"},
{"id":20, "name":"David", "venue":{"id":14, "town":"Southampton"}, "month":"June"},
{"id":17, "name":"Mary", "venue":{"id":56, "town":"London"}, "month":"December"}]

列表中的条目数最多为100。对于以伦敦为城镇的条目，我计划为每个条目显示“名称”，一次给出一个结果。其余的对我毫无用处。我是python的初学者，所以我对如何有效地解决此问题提出了建议。最初，我认为最好删除所有没有伦敦的条目，然后再逐个进行审核。

我还想知道是否不进行过滤而是循环遍历整个json并选择具有该镇作为伦敦的条目的名称是否更快。

Answer 1

您可以使用filter：

data = [{"id":13, "name":"Albert", "venue":{"id":123, "town":"Birmingham"}, "month":"February"},
        {"id":17, "name":"Alfred", "venue":{"id":456, "town":"London"}, "month":"February"},
        {"id":20, "name":"David", "venue":{"id":14, "town":"Southampton"}, "month":"June"},
        {"id":17, "name":"Mary", "venue":{"id":56, "town":"London"}, "month":"December"}]

london_dicts = filter(lambda d: d['venue']['town'] == 'London', data)
for d in london_dicts:
    print(d)

这是有效率的，因为：

循环是用C语言编写的（对于CPython，则是这样）
filter返回一个迭代器（在Python 3中），这意味着结果将按要求一一加载到内存中。

Answer 2

一种方法是使用列表理解：

>>> data = [{"id":13, "name":"Albert", "venue":{"id":123, "town":"Birmingham"}, "month":"February"},
            {"id":17, "name":"Alfred", "venue":{"id":456, "town":"London"}, "month":"February"},
            {"id":20, "name":"David", "venue":{"id":14, "town":"Southampton"}, "month":"June"},
            {"id":17, "name":"Mary", "venue":{"id":56, "town":"London"}, "month":"December"}]

>>> [d for d in data if d['venue']['town'] == 'London']
[{'id': 17,
  'name': 'Alfred',
  'venue': {'id': 456, 'town': 'London'},
  'month': 'February'},
 {'id': 17,
  'name': 'Mary',
  'venue': {'id': 56, 'town': 'London'},
  'month': 'December'}]

通过带有嵌入式词典的列表进行过滤

2 个答案: