Exclude empty/null values from JSON serialization

Question

I am serializing multiple nested dictionaries to JSON using Python with simplejson.

Is there any way to automatically exclude empty/null values?

For example, serialize this:

 {
     "dict1" : {
     "key1" : "value1",
     "key2" : None
     }
 }

to

 {
     "dict1" : {
     "key1" : "value1"
     }
 }

When using Jackson with Java you can use Inclusion.NON_NULL to do this. Is there a simplejson equivalent?

Solution 1

def del_none(d):
    """
    Delete keys with the value ``None`` in a dictionary, recursively.

    This alters the input so you may wish to ``copy`` the dict first.
    """
    # For Python 3, write `list(d.items())`; `d.items()` won’t work
    # For Python 2, write `d.items()`; `d.iteritems()` won’t work
    for key, value in list(d.items()):
        if value is None:
            del d[key]
        elif isinstance(value, dict):
            del_none(value)
    return d  # For convenience

Sample usage:

>>> mydict = {'dict1': {'key1': 'value1', 'key2': None}}
>>> print(del_none(mydict.copy()))
{'dict1': {'key1': 'value1'}}

Then you can feed that to json.

Solution 2

My Python3 version of this has the benefit of not changing the input, as well as recursion into dictionaries nested in lists:

def clean_nones(value):
    """
    Recursively remove all None values from dictionaries and lists, and returns
    the result as a new dictionary or list.
    """
    if isinstance(value, list):
        return [clean_nones(x) for x in value if x is not None]
    elif isinstance(value, dict):
        return {
            key: clean_nones(val)
            for key, val in value.items()
            if val is not None
        }
    else:
        return value

For example:

a = {
    "a": None,
    "b": "notNone",
    "c": ["hello", None, "goodbye"],
    "d": [
        {
            "a": "notNone",
            "b": None,
            "c": ["hello", None, "goodbye"],
        },
        {
            "a": "notNone",
            "b": None,
            "c": ["hello", None, "goodbye"],
        }
    ]
}


print(clean_nones(a))

results in this:

{
    'b': 'notNone',
    'c': ['hello', 'goodbye'],
    'd': [
        {
            'a': 'notNone',
            'c': ['hello', 'goodbye']
        },
        {
            'a': 'notNone',
            'c': ['hello', 'goodbye']
        }
    ]
}

Solution 3

>>> def cleandict(d):
...     if not isinstance(d, dict):
...         return d
...     return dict((k,cleandict(v)) for k,v in d.iteritems() if v is not None)
... 
>>> mydict = dict(dict1=dict(key1='value1', key2=None))
>>> print cleandict(mydict)
{'dict1': {'key1': 'value1'}}
>>> 

I don't like using del in general, changing the existing dictionary can have subtle effects depending on how they are created. Creating new dictionaries with None removed prevents all side effect.

Solution 4

You can try this approach. In my case (I use python 3), it works well.

def to_json(self):
    return json.dumps(self,
                      default=lambda o: dict((key, value) for key, value in o.__dict__.items() if value),
                      indent=4,
                      allow_nan=False)

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