Example of how to exclude Nones from JSON-encoded output, optionally destructively

filter_nones.py

#!/usr/bin/env python3
"""
Example of how to non-destructively remove None values from an object before
JSON serialization
"""

import json


def filter_nones(obj):
    """
    Given a JSON-serializable object, return a copy without elements which have
    a value of None.
    """

    if isinstance(obj, list):
        # This version may or may not be easier to read depending on your
        # preferences:
        # return list(filter(None, map(remove_nones, obj)))

        # This version uses a generator expression to avoid computing a full
        # list only to immediately walk it again:
        filtered_values = (filter_nones(j) for j in obj)
        return [i for i in filtered_values if i is not None]
    elif isinstance(obj, dict):
        filtered_items = ((i, filter_nones(j)) for i, j in obj.items())
        return {k: v for k, v in filtered_items if v is not None}
    else:
        return obj

def remove_nones(obj):
    """
    Given a JSON-serializable object, modify it in place to remove elements
    which have a value of None
    """

    if isinstance(obj, list):
        # We can't use list.remove() while iterating because that will cause the
        # next element in the list to be skipped.

        # Slice assignment alters the list in-place in case there are any other
        # references to it:
        # for i in obj:
        #     remove_nones(i)
        # obj[:] = [i for i in obj if i is not None]

        # … or we can walk the list in reverse to avoid a second pass:
        for i in range(len(obj) - 1, -1, -1):
            v = obj[i]
            if v is None:
                obj.pop(i)
            else:
                remove_nones(v)

    elif isinstance(obj, dict):
        # We're forced to create a list first to avoid an exception caused by
        # changing the dictionary size while iterating:
        for k, v in list(obj.items()):
            if v is None:
                obj.pop(k)
            else:
                remove_nones(v)


resp = {
    "scalar": "test",
    "list": ["foo", None, "bar"],
    "nested_dict": {
        "a": 1,
        "b": ["test", None, "test2"],
        "d": None,
        "e": [
            None,
            {
                "k": None,
                "a": "b",
            },
        ],
    },
    "scalar2": None,
    "nested_list": [
        "foo",
        [None],
        ["bar", "baaz"],
    ],
}

print(json.dumps(resp, indent=4))
print(json.dumps(filter_nones(resp), indent=4))

remove_nones(resp)
print(json.dumps(resp, indent=4))