如何在python中更新字典值？

Question

假设我有一本如下所示的词典：

dict1 = {band1Review: ["good rhythm", "cool performance"], band2Review: ["fast tempo", "too loud"]}
band1Review = ["Not good", "terrible"]
band3Review = ["best band ever"]

如果我知道我有这两个新的评论，有没有一种方法可以让我现有的字典看起来像下面这样？你知道吗

dict1 = {band1Review: ["good rhythm", "cool performance", "Not good", "terrible"], band2Review: ["fast tempo", "too loud"], band3Review: ["best band ever"]}

我也希望这样做有效率，没有乏味的循环，可能会减慢我的程序。有什么建议吗？你知道吗

Answer 1

字典中存储的列表是可变的，可以就地更新。例如，可以使用append附加单个项：

>>> container = {"a": [1, 2], "b": [4, 5]}
>>> container["a"]
[1, 2]
>>> container["a"].append(3)
>>> container["a"]
[1, 2, 3]

一切都很好。您声明希望避免“冗长”的循环；我不太清楚这意味着什么，但您当然可以使用list类型上的extend方法避免循环：

>>> newb = [6, 7, 8]
>>> container["b"].extend(newb)
>>> container["b"]
[4, 5, 6, 7, 8]

Answer 2

dict1 = {"band1": ["good rhythm", "cool performance"], "band2": ["fast tempo", "too loud"]}
band1Review = ["Not good", "terrible"]
band3Review = ["best band ever"]

dict1.setdefault("band1", []).extend(band1Review)
dict1.setdefault("band3Review", []).extend(band3Review)
print dict1

结果：

{'band1': ['good rhythm', 'cool performance', 'Not good', 'terrible'], 'band2': ['fast tempo', 'too loud'], 'band3Review': ['best band ever']}