JSON serialize a class and change property casing with Python

Question

I'd like to create a JSON representation of a class and change the property names automatically from snake_case to lowerCamelCase, as I'd like to comply with PEP8 in Python and also the JavaScript naming conventions (and maybe even more importantly, the backend I'm communicating to uses lowerCamelCase).

I prefer to use the standard json module, but I have nothing against using another, open source library (e.g. jsonpickle might solve my issue?).

>>> class HardwareProfile:
...     def __init__(self, vm_size):
...             self.vm_size = vm_size
>>> hp = HardwareProfile('Large')
>>> hp.vm_size
'Large'
### ### What I want ### ###
>>> magicjson.dumps(hp)
'{"vmSize": "Large"}'
### ### What I have so far... ### ###
>>> json.dumps(hp, default=lambda o: o.__dict__)
'{"vm_size": "Large"}'

Answer 1

You just need to create a function to transform the snake_case keys to camelCase. You can easily do that using .split, .lower, and .title.

import json

class HardwareProfile:
    def __init__(self, vm_size):
        self.vm_size = vm_size
        self.some_other_thing = 42
        self.a = 'a'

def snake_to_camel(s):
    a = s.split('_')
    a[0] = a[0].lower()
    if len(a) > 1:
        a[1:] = [u.title() for u in a[1:]]
    return ''.join(a)

def serialise(obj):
    return {snake_to_camel(k): v for k, v in obj.__dict__.items()}

hp = HardwareProfile('Large')
print(json.dumps(serialise(hp), indent=4, default=serialise))

output

{
    "vmSize": "Large",
    "someOtherThing": 42,
    "a": "a"
}

You could put serialise in a lambda, but I think it's more readable to write it as a proper def function.