在Python中动态创建嵌套字典 [英] Create nested dictionary on the fly in Python

问题描述

试图了解如何动态创建嵌套字典.理想情况下，我的字典应类似于:

Trying to understand how to create nested dictionaries on the fly. Ideally my dictionary would look something like:

mydict = { 'Message 114861156': { 'email': ['[e-mail]', '[e-mail]'] }, { 'status': 'Queued mail for delivery' }} 

这是我到目前为止所拥有的:

Here's what i have so far:

sampledata = "Message 114861156 to [e-mail] [e-mail]  [InternalId=260927844] Queued mail for delivery'."

makedict(sampledata)

def makedict(results):
  newdict = {}
  for item in results:
    msgid = re.search(r'Message \d+', item)
    msgid = msgid.group()
    newdict[msgid]['emails'] = re.findall(r'\w+@\w+\.\w+', item)
    newdict[msgid]['status'] = re.findall(r'Queued mail for delivery', item)

具有以下输出:

Traceback (most recent call last):
  File "wildfires.py", line 57, in <module>
    striptheshit(q_result)
  File "wildfires.py", line 47, in striptheshit
    newdict[msgid]['emails'] = re.findall(r'\w+@\w+\.\w+', item)
KeyError: 'Message 114861156'

如何动态制作像这样的嵌套字典?

How do you make a nested dictionary like this on the fly?

推荐答案

dict.setdefault是一个很好的工具，collections.defaultdict

dict.setdefault is a good tool, so is collections.defaultdict

您现在的问题是newdict是一个空字典，因此newdict[msgid]引用了不存在的键.这在分配事物(newdict[msgid] = "foo")时有效，但是由于newdict[msgid]最初未设置为 的任何内容，因此当您尝试对其进行索引时，会得到一个KeyError.

Your problem right now is that newdict is an empty dictionary, so newdict[msgid] refers to a non-existent key. This works when assigning things (newdict[msgid] = "foo"), however since newdict[msgid] isn't set to anything originally, when you try to index it you get a KeyError.

dict.setdefault让您回避最初说如果newdict中存在msgid，请给我其值.如果不存在，请将其值设置为{}并给我.

dict.setdefault lets you sidestep that by initially saying "If msgid exists in newdict, give me its value. If not, set its value to {} and give me that instead.

def makedict(results):
    newdict = {}
    for item in results:
        msgid = re.search(r'Message \d+', item).group()
        newdict.setdefault(msgid, {})['emails'] = ...
        newdict[msgid]['status'] = ...
        # Now you KNOW that newdict[msgid] is there, 'cuz you just created it if not!

使用collections.defaultdict可以节省调用dict.setdefault的步骤. defaultdict用要调用的函数初始化，该函数生成一个容器，该容器将任何不存在的键都分配为值，例如

Using collections.defaultdict saves you the step of calling dict.setdefault. A defaultdict is initialized with a function to call that produces a container that any non-existent key gets assigned as a value, e.g.

from collections import defaultdict

foo = defaultdict(list)
# foo is now a dictionary object whose every new key is `list()`
foo["bar"].append(1)  # foo["bar"] becomes a list when it's called, so we can append immediately

您可以这样说:嘿，如果我与您谈论新的msgid，我希望它成为一本新的词典.

You can use this to say "Hey if I talk to you about a new msgid, I want it to be a new dictionary.

from collections import defaultdict

def makedict(results):
    newdict = defaultdict(dict)
    for item in results:
        msgid = re.search(r'Message \d+', item).group()
        newdict[msgid]['emails'] = ...
        newdict[msgid]['status'] = ...

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