json-fix

What is this?

A pip module that let you define a __json__ method, that works like the toJSON from JavaScript.
(e.g. it magically gets called whenever someone does json.dumps(your_object))

From a technical perspective, this module is a safe, backwards-compatible, reversable patch to the built-in python json object that allows classes to specify how they should be serialized.

Why?

Because sometimes external code uses something like

import json
json.dumps(list_containing_your_object)

And it simply throws an error no matter how you customize your object

How do I use this for my class?

pip install json-fix

import json_fix # import this before the JSON.dumps gets called

# same file, or different file
class YOUR_CLASS:
    def __json__(self):
        # YOUR CUSTOM CODE HERE
        #    you probably just want to do:
        #        return self.__dict__
        return "a built-in object that is natually json-able"

How do I change how someone elses class is jsonified?

There's 2 ways; the aggressive override_table or the more collaboration-friendly fallback_table. Some really powerful stuff can be done safely with the fallback table.

Override Table

If a pip module defines a class, you can control how it is json-dumped, even if they defined a .__json__() method, by using json.override_table.

• Note! The "when" (in when-a-rule-is-added) can be very important. Whatever rule was most-recently added will have the highest priority. So, even if a pip module uses the override table, you can override their override by doing import that_module and THEN adding your rule to the override table.
• Note 2! The override table is capable of changing how built-in types are dumped, be careful!

import json_fix # import this before the JSON.dumps gets called
import json
import pandas as pd

SomeClassYouDidntDefine = pd.DataFrame

# create a boolean function for identifying the class
class_checker = lambda obj: isinstance(obj, SomeClassYouDidntDefine)
# then assign it to a function that does the converting
json.override_table[class_checker] = lambda obj_of_that_class: json.loads(obj_of_that_class.to_json())

json.dumps([ 1, 2, SomeClassYouDidntDefine() ], indent=2) # dumps as expected

Fallback Table

Let's say we want all python classes to be jsonable by default, well we can easily do that with the fallback table. The logic is if notthing in override table, and no .__json__ method, then check the fallback table.

import json_fix # import this before the JSON.dumps gets called
import json

# a checker for custom objects
checker = lambda obj: hasattr(obj, "__dict__")
# use the __dict__ when they don't specify a __json__ method 
json.fallback_table[checker] = lambda obj_with_dict: obj_with_dict.__dict__

class SomeClass:
    def __init__(self):
        self.thing = 10

json.dumps([ 1, 2, SomeClass() ], indent=2) # dumps as expected

Like the override table, the most recently-added checker will have the highest priority.