将字符串映射到一组字符串的Python字典？ [英] Python dictionary that maps strings to a set of strings?

问题描述

我想使用一个Python字典作为键和字符串作为值的字符串。例如： {crackers：[crunchy，salty]} 它必须是一个集合，而不是列表。

I would like to be able to make a Python dictionary with strings as keys and sets of strings as the values. E.g.: { "crackers" : ["crunchy", "salty"] } It must be a set, not a list.

但是，当我尝试以下内容：

However, when I try the following:

  word_dict = dict()
  word_dict["foo"] = set()
  word_dict["foo"] = word_dict["foo"].add("baz")                                    
  word_dict["foo"] = word_dict["foo"].add("bang")

我得到：

Traceback (most recent call last):
  File "process_input.py", line 56, in <module>
    test()
  File "process_input.py", line 51, in test
    word_dict["foo"] = word_dict["foo"].add("bang")
AttributeError: 'NoneType' object has no attribute 'add'

如果我这样做：

  word_dict = dict()
  myset = set()
  myset.add("bar")
  word_dict["foo"] = myset
  myset.add("bang")
  word_dict["foo"] = myset

  for key, value in word_dict:                                                       
      print key,                                                                
      print value

我得到：

Traceback (most recent call last):
  File "process_input.py", line 61, in <module>
    test()
  File "process_input.py", line 58, in test
    for key, value in word_dict:
ValueError: too many values to unpack

有关如何强制Python做任何我想要的任何提示？我是一个中间Python用户（或者我以为，直到我遇到这个问题。）

Any tips on how to coerce Python into doing what I'd like? I'm an intermediate Python user (or so I thought, until I ran into this problem.)

推荐答案

set.add（）不会返回一个新的集，它修改集它被调用。以这种方式使用：

set.add() does not return a new set, it modifies the set it is called on. Use it this way:

word_dict = dict()
word_dict["foo"] = set()
word_dict["foo"].add("baz")                                    
word_dict["foo"].add("bang")

另外，如果您使用循环的循环使用dict，那么您将迭代键：

Also, if you use a for loop to iterate over a dict, you are iterating over the keys:

for key in word_dict:
   print key, word_dict[key]

或者您可以迭代 word_dict.items（）或 word_dict.iteritems（）：

for key, value in word_dict.items():
   print key, value

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