您何时会在dict.update方法的字典上使用键值对? [英] When would you use a key-value pair over a dict for the dict.update method?
问题描述
我注意到您可以做两件事来更新字典,并且它们似乎具有相同的结果:
I've noticed that you can do two things to update a dictionary, and that they seem to have the same outcome:
a = {}
a.update({'foo': 1})
a = {}
a.update(foo = 1)
两者都导致字典的结果如下:
Both lead to the result of a dictionary that looks like:
{'foo': 1}
是否有任何理由更喜欢使用字典或键/值对作为更新方法?它们在功能上是完全等效的还是一种语法可能导致的陷阱"?
Is there any reason to prefer using a dictionary or a key/value pair for the update method? Are they completely functionally equivalent or is there a 'gotcha' that one syntax might cause?
推荐答案
使用一个使用另一个可能是不同的原因.例如:
There could be different reasons for using one over the other. For example:
>>> d = {}
>>> d.update(a=2) # looks much cleaner
>>> d.update({'a': 2}) # We need to unnecessarily write a few more characters,
但是再说一次,如果我想更新str类型以外的其他键:
But then again, if I want to update a key other than of str type:
>>> d = {}
>>> d.update(2='a') # Gives a syntax error
>>> d.update({2: 'a'}) # is the only way
此外,您可以存储 dict
,因此,如果需要通过变量进行更新:
Furthermore, you can store a dict
, so if you needed to update via a variable:
>>> u = {'a': 2}
>>> d = {}
>>> d.update(u) # clean
>>> d.update(**u) # Essentially same as using keyword argument form, but unnecessary
另一种情况是,当您手动更新某些键,但从变量中更新其他键时,关键字参数形式更简洁:
Another scenario, when you are updating some key manually, but others from a variable, keyword argument form is cleaner and shorter:
>>> u = {'a': 2}
>>> d = {}
>>> d.update(b=3, **u)
# Whereas to use `dict` form:
>>> d.update({'b': 3, **u}) # Introduces unnecessary clutter
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