In JavaScript, null represents the absence of a value. It means nothing. The Python equivalent to null is None.

When you parse the json data to Python objects, null becomes None. To handle the JSON null, you can use the json.loads() or json.load() method (when working with files).

import json

# Example JSON string with null
json_string = '{"name": "Calvin", "age": null, "country": "USA"}'

# Parsing JSON string
python_data = json.loads(json_string)

print(python_data)

# Output: {'name': 'Calvin', 'age': None, 'country': 'USA'}

You can see from the above output that null is automatically converted to None.

Serializing Python to JSON

If you have a Python object and want to serialize it to json, you can use the json.dumps() method. After converting to json values, None becomes null automatically.

import json

python_dict = {"name": "Calvin", "age": None, "country": "USA"}

# Parsing Python dictionary
json_obj = json.dumps(python_dict)

print(json_obj)

# Output: {"name": "Calvin", "age": null, "country": "USA"}

Handling Non-Serializable Types (e.g., NaN)

JSON standard has no direct equivalent of Python’s NaN. However, you can still display a NaN value (along with Infinity and -Infinity if present) as it is in a JSON object by setting the allow_nan argument to True in the json.dumps() method.

import json
import math

data = {'value': math.nan}
json_str = json.dumps(data, allow_nan=True)

print(json_str)

# Output: {"value": NaN}

And we get the NaN in the JSON standard.

Replacing null with Default Values

You need to define a custom function that accepts a Python object and a default value. Then convert all the None values to the default values.

import json

def replace_none(obj, default):
    if isinstance(obj, dict):
        return {k: replace_none(v, default) for k, v in obj.items()}
    elif isinstance(obj, list):
        return [replace_none(elem, default) for elem in obj]
    return obj if obj is not None else default

python_obj = json.loads('{"name": null}')

processed = replace_none(python_obj, 'default')

print(processed)

# Output: {'name': 'default'}

In this code, first, we load the json data into a Python object using the json.loads() method. 

In the next step, we passed that object to the custom replace_none() method. This custom method returns the “default” value instead of None values because we replaced the default with it.

That’s all!