Python中是否有“multimap”实现？ [英] Is there a 'multimap' implementation in Python?

问题描述

我是Python的新手，我熟悉 Multimaps 在其他 语言。 Python是否具有内置的这种数据结构，或者在常用的库中可用？

I am new to Python, and I am familiar with implementations of Multimaps in other languages. Does Python have such a data structure built-in, or available in a commonly-used library?

为了说明multimap的含义：

To illustrate what I mean by "multimap":

a = multidict()
a[1] = 'a'
a[1] = 'b'
a[2] = 'c'

print(a[1])  # prints: ['a', 'b']
print(a[2])  # prints: ['c']

推荐答案

这样的事情不存在于标准库。您可以使用 defaultdict 虽然：

Such a thing is not present in the standard library. You can use a defaultdict though:

>>> from collections import defaultdict
>>> md = defaultdict(list)
>>> md[1].append('a')
>>> md[1].append('b')
>>> md[2].append('c')
>>> md[1]
['a', 'b']
>>> md[2]
['c']

（而不是列表您可能需要使用设置，在这种情况下，您可以调用 .add 而不是 .append 。）

(Instead of list you may want to use set, in which case you'd call .add instead of .append.)

As另见：看看你写的这两行：

As an aside: look at these two lines you wrote:

a[1] = 'a'
a[1] = 'b'

这似乎表明你想要表达式 a [1] 等于两个不同的值。字典是不可能的，因为它们的键是唯一的，它们中的每一个都与一个值相关联。然而，您可以可以逐个提取与给定键相关联的列表内的所有值。您可以使用 iter ，然后连续调用 next 。或者你可以使用两个循环：

This seems to indicate that you want the expression a[1] to be equal to two distinct values. This is not possible with dictionaries because their keys are unique and each of them is associated with a single value. What you can do, however, is extract all values inside the list associated with a given key, one by one. You can use iter followed by successive calls to next for that. Or you can just use two loops:

>>> for k, v in md.items():
...     for w in v:
...         print("md[%d] = '%s'" % (k, w))
... 
md[1] = 'a'
md[1] = 'b'
md[2] = 'c'

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