Problems while parsing a nested json/list in python3?

Question

I have a very large list alist which has a dict and a nested list like this:

a_list = [{'A': [], 's': {'code': '0', 'credits': '0', 'msg': 'OK'}},
 {'A': [{'dictionary': 'True',
    'item': 'pineapples',
    'id': '13',
    'score': '9.7899',
    'rollup': {'True': 'OK', 'Fiz': 'Yes'},
    'variant_list': [{'endp': '8', 'form': 'pineapple', 'register': '0'}]}], 'status': {'codecheck': '0', 'cred': '90809890', 'msg': 'OK'}},
......

{'A': [], 's': {'code': '0', 'credits': '0', 'msg': 'OK'}},
    ]

How can I extract the extract the item parameter if and only if exist into a list like this:

['NaN', 'pineapples', 'NaN']

I do not understand how to parse it since it has a very nested structure, the main issue which I am struggling with is to accessing to each element of the list and then to the other list and leaving a NaN string.

@RomanPerekhrest thanks for the help!, as you can see in the first and the third element of a_list they have just an empty list {'A': [], 's': {'code': '0', 'credits': '0', 'msg': 'OK'}} I would like to impute a NaN there, since it has a void list. — john doe
– john doe, Commented Jan 19, 2017 at 19:28
@tooty44, yes for instance just replace this {'A': [], 's': {'code': '0', 'credits': '0', 'msg': 'OK'}}, for NaN — john doe
– john doe, Commented Jan 19, 2017 at 19:29

RomanPerekhrest · Accepted Answer · 2017-01-19 19:42:58Z

1

Use the following approach(list comprehension):

a_list = [{'A': [], 's': {'code': '0', 'credits': '0', 'msg': 'OK'}},
          {'A': [{'dictionary': 'True',
                  'item': 'pineapples',
                  'id': '13',
                  'score': '9.7899',
                  'rollup': {'True': 'OK', 'Fiz': 'Yes'},
                  'variant_list': [{'endp': '8', 'form': 'pineapple', 'register': '0'}]}],
           'status': {'codecheck': '0', 'cred': '90809890', 'msg': 'OK'}},
          {'A': [], 's': {'code': '0', 'credits': '0', 'msg': 'OK'}},
          ]

result = ['NaN' if not len(o['A']) else o['A'][0]['item'] for o in a_list]
print(result)

The output:

['NaN', 'pineapples', 'NaN']

List comprehensions provide a concise way to create lists. Common applications are to make new lists where each element is the result of some operations applied to each member of another sequence or iterable, or to create a subsequence of those elements that satisfy a certain condition.

a certain condition, in your case, is 'NaN' if not len(o['A']) else o['A'][0]['item']

https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions

edited Jan 19, 2017 at 19:42

answered Jan 19, 2017 at 19:37

RomanPerekhrest

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1 Comment

john doe Over a year ago

Could you provide some explanation?.. I didnot understood pretty well the list comprehension.

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