在python中更新字典 [英] Updating a dictionary in python

问题描述

我在这个问题上停留了很长时间，无法解决。我只想了解我所缺少的内容以及为什么需要它。
我需要做的是制作一个函数，将每个给定的键/值对添加到字典中。参数key_value_pairs将是形式为（键，值）的元组列表。

I've been stuck on this question for quite sometime and just can't figure it out. I just want to be able to understand what I'm missing and why it's needed. What I need to do is make a function which adds each given key/value pair to the dictionary. The argument key_value_pairs will be a list of tuples in the form (key, value).

def add_to_dict(d, key_value_pairs):

    newinputs = [] #creates new list
    for key, value in key_value_pairs:
        d[key] = value #updates element of key with value
        if key in key_value_pairs:
            newinputs.append((d[key], value)) #adds d[key and value to list
    return newinputs

我不知道给出了当d和key_value_pairs具有不同的键时如何更新值变量的方法。

I can't figure out how to update the "value" variable when d and key_value_pairs have different keys.

这些方案中的前三种有效，但其余方案都失败了

The first three of these scenarios work but the rest fail

>>> d = {}
>>> add_to_dict(d, [])
[]
>>> d
{}

>>> d = {}
>>> add_to_dict(d, [('a', 2])
[]
>>> d
{'a': 2}

>>> d = {'b': 4}
>>> add_to_dict(d, [('a', 2)])
[]
>>> d
{'a':2, 'b':4}

>>> d = {'a': 0}
>>> add_to_dict(d, [('a', 2)])
[('a', 0)]
>>> d
{'a':2}

>>> d = {'a', 0, 'b': 1}
>>> add_to_dict(d, [('a', 2), ('b': 4)])
[('a', 2), ('b': 1)]
>>> d
{'a': 2, 'b': 4}

>>> d = {'a': 0}
>>> add_to_dict(d, [('a', 1), ('a': 2)])
[('a', 0), ('a':1)]
>>> d
{'a': 2}

谢谢

已编辑。

推荐答案

Python内置了此功能：

Python has this feature built-in:

>>> d = {'b': 4}
>>> d.update({'a': 2})
>>> d
{'a': 2, 'b': 4}

或者如果您不被允许使用 dict.update ：

Or given you're not allowed to use dict.update:

>>> d = dict(d.items() + {'a': 2}.items())   # doesn't work in python 3

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