Capture python value from multi-nested dictionary

问题

I'm having some problems obtaining a variable from a multi-nested dictionary.

I'm trying to grab CategoryParentID with the following snippet:

print dicstr['CategoryParentID']

while my dictionary looks like this:

{
    "CategoryCount": "12842",
    "UpdateTime": "2018-04-10T02:31:49.000Z",
    "Version": "1057",
    "Ack": "Success",
    "Timestamp": "2018-07-17T18:33:40.893Z",
    "CategoryArray": {
        "Category": [
            {
                "CategoryName": "Antiques",
                "CategoryLevel": "1",
                "AutoPayEnabled": "true",
                "BestOfferEnabled": "true",
                "CategoryParentID": "20081",
                "CategoryID": "20081"
            },
.
.
.
}

I'm getting this error, however:

Traceback (most recent call last):
  File "get_categories.py", line 25, in <module>
    getUser()
  File "get_categories.py", line 18, in getUser
    print dictstr['CategoryParentID']
KeyError: 'CategoryParentID'

回答1:

You need to first traverse the dictionary. CategoryParentID is in a list (hence [0]) which is a value of Category which is a value of CategoryArray

dicstr = {'CategoryCount': '12842',
 'UpdateTime': '2018-04-10T02:31:49.000Z',
 'Version': '1057',
 'Ack': 'Success',
 'Timestamp': '2018-07-17T18:33:40.893Z',
 'CategoryArray': {'Category': [{'CategoryName': 'Antiques',
    'CategoryLevel': '1',
    'AutoPayEnabled': 'true',
    'BestOfferEnabled': 'true',
    'CategoryParentID': '20081',
    'CategoryID': '20081'}]
      }
  }

dicstr['CategoryArray']['Category'][0]['CategoryParentID']
'20081'

回答2:

You'll have to get it like -

x['CategoryArray']['Category'][0]['CategoryParentID']

If we simplify the dict you posted, we get -

d = {'CategoryArray': {'Category': [{'CategoryParentID': '20081'}]}}
# "CategoryArray" 
# "Category" child of CategoryArray 
#  Key "Category" contains a list [{'CategoryName': 'Antiques', 'CategoryParentID': '20081'...}]
#  Get 0th element of key "Category" and get value of key ["CategoryParentID"]

I hope it makes sense

回答3:

When you ask Python to give you dicstr['CategoryParentID'], what you're asking it to do is to give you the value that's associated with the key 'CategoryParentID' in dicstr.

Look at the way your dictionary is defined. The keys of dictstr are going to be all the keys that are exactly one level under dictstr. These are the keys Python is looking at to try to find CategoryParentID when you specify dictstr['CategoryParentID']. These keys are:

"CategoryCount"

"UpdateTime"

"Version"

"Ack"

"Timestamp"

"CategoryArray"

Notice that the key you're looking for isn't there. That's because it's nested several levels deeper in dictstr. You need to keep "hopping along" these keys until you get to the CategoryParentID key. Try:

dictstr['CategoryArray']['Category'][0]['CategoryParentID']

Note the [0] in there. The value that's associated with the 'Category' key is a list. That list contains one element, which is a dictionary. In order to get to the dictionary, which holds the key you actually want, you have to index into the list at the index that holds the dictionary. Since there's only one element, index directly into it using [0] to get the dictionary, and then continue to "hop along" the keys.

来源：https://stackoverflow.com/questions/51389749/capture-python-value-from-multi-nested-dictionary

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