Python 创建或附加到字典中的列表 - 可以缩短吗？
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Create or append to a list in a dictionary - can this be shortened?
提问by culebrón
Can this Python code be shortened and still be readable using itertools and sets?
可以使用 itertools 和 set 缩短此 Python 代码并仍然可读吗？
result = {}
for widget_type, app in widgets:
if widget_type not in result:
result[widget_type] = []
result[widget_type].append(app)
I can think of this only:
我只能想到这个：
widget_types = zip(*widgets)[0]
dict([k, [v for w, v in widgets if w == k]) for k in set(widget_types)])
采纳答案by Mark Byers
You can use a defaultdict(list).
您可以使用一个defaultdict(list).
from collections import defaultdict
result = defaultdict(list)
for widget_type, app in widgets:
result[widget_type].append(app)
回答by Daniel Roseman
An alternative to defaultdictis to use the setdefaultmethod of standard dictionaries:
另一种方法defaultdict是使用setdefault标准词典的方法：
result = {}
for widget_type, app in widgets:
result.setdefault(widget_type, []).append(app)
This relies on the fact that lists are mutable, so what is returned from setdefault is the same list as the one in the dictionary, therefore you can append to it.
这依赖于列表是可变的这一事实，因此从 setdefault 返回的列表与字典中的列表相同，因此您可以附加到它。
回答by user1139002
may be a bit slow but works
可能有点慢但有效
result = {}
for widget_type, app in widgets:
result[widget_type] = result.get(widget_type, []) + [app]
