Referencing parent object instance from inner class

Question

I'm trying to create a syntax friendly library that doesn't require the user to constantly pass in credentials or type redundant or excessive statements. My strategy is to focus on how I intend the library syntax to look, and then design the library to function in that way. I know I can implement the following:

api = Api(user="admin", pswd="blahblah")

new_order = api.Order()
new_order.status = "pending"
api.create(new_order)
api.order_assign_user(new_order, user)

existing_order = api.get_order(orderId=12345)
existing_order.status = "shipped"
api.update(existing_order)

using something like the following:

class Api(object):
    def __init__(self, user=None, pswd=None):
        self.user = user
        self.pswd = pswd

    class Order(api):
        def __init__ (self, status=None):
            self.status = status

    def create(self, x):
        auth = Auth(self.user, self.pswd)
        # use authorization credentials to create data remotely
        return x

    def update(self, x):
        auth = Auth(self.user, self.pswd)
        # use authorization credentials to update data from remote
        return x

    def get_order(self, orderId=None):
        auth = Auth(self.user, self.pswd)
        # use authorization credentials to update data from remote
        return order

But I'd like to be able to use the following statements:

new_order.create() # instead of api.create(new_order)

new_order.assign_user(user) # instead of api.order_assign_user(new_order, user)

existing_order = api.Order.get(orderId=12345) # returns retrieved Order Instance

Which presents me with a problem:

How would I get the Order() instance to access attributes of the Api() instance that created it? Without access to these, any attributes like 'user' and 'pswd' would be inaccessible (they're needed for requests.get() calls)

I've tried variations of functions and classes to accomplish this, but could never solve this problem. This is the closest I've been able to achieve:

class Api(object):
    def __init__(self, user=None, pswd=None):
        self.user = user
        self.pswd = pswd

    class Order(api):
        def __init__ (self, status=None):
            self.status = status

        @classmethod
        def get(cls, value):
            return cls(status=value)

        def create(self):
            auth = Auth(self.user, self.pswd) 
            # these credentials need to come from the Api() instance?, not self
            return x

        def update(self):
            auth = Auth(self.user, self.pswd) 
            # these credentials need to come from the Api() instance?, not self
            return x

Is this possible? Or am I going about this the wrong way? I've considered making this into a module but that didn't seem to be a valid option either.

It's possible but I don't have time for a proper answer right now, I'll come back later to answer if no one has posted yet, meanwhile take a look at the __get__ and __set__ magic methods and how they receive an instance parameter, you can instantiate your Order class inside your Api class and leverage this methods — Dalvenjia
– Dalvenjia, Commented Sep 5, 2018 at 21:51

Dalvenjia · Accepted Answer · 2018-09-06 02:14:01Z

1

This demonstrates a basic implementation of what I think you want to do, I found this better than the __get__, __set__ hackery that I had in mind when I commented your question

import requests

class Order:
    def __init__(self, user:str, passwd: str):
        self.session = requests.Session()
        self.session.auth = (user, passwd)
        self.status = None

    # This is only to make the class callable, since the class is
    # already instantiated in Api init calling it again would raise an exception
    def __call__(self, **kwargs):
        for key, value in kwargs.items():
            setattr(self, key, value)
        return self

    def get(self):
        response = self.session.get('https://httpbin.org/basic-auth/my_user/my_pass')
        print(response.text)

    def post(self):
        response = self.session.post('https://httpbin.org/post', data={'status': self.status})
        print(response.text)


class Api:
    def __init__(self, user: str, passwd: str):
        self.Order = Order(user, passwd)

answered Sep 6, 2018 at 2:14

Dalvenjia

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1 Comment

LegendaryJLD Over a year ago

I was able to use this to accomplish exactly what I wanted. Thank you.

Mikhail Burshteyn · Accepted Answer · 2018-09-05 20:55:01Z

1

Inner classes in Python are just separate classes, and their instances are not in any way automatically associated with an instance of an outer class.

I would suggest a solution in which the constructor of Order would take an Api instance as an argument and work with that instance:

class Api(object):
    def __init__(self, user=None, pswd=None):
        self.user = user
        self.pswd = pswd

class Order(object):
    def __init__(self, api, status=None):
        self.api = api
        self.status = status

    @classmethod
    def get(cls, api, value):
        return cls(api, status=value)

    def create(self):
        auth = Auth(self.api.user, self.api.pswd)
        return x

    def update(self):
        auth = Auth(self.api.user, self.api.pswd)
        return x

answered Sep 5, 2018 at 20:55

Mikhail Burshteyn

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4 Comments

LegendaryJLD Over a year ago

This would work, but then I would have to type Order.get(api, orderId=12345) which while not super problematic, isn't the goal I'm trying to accomplish. Although it seems something like this might end up being my solution.

Mikhail Burshteyn Over a year ago

If I were you, I would make a get_order method in the Api class which would return Order(api=self, ...) and then work with that order.

Mikhail Burshteyn Over a year ago

On an unrelated note, camelCased names (like orderId in your comment) are not pythonic, you should use snake_case.

LegendaryJLD Over a year ago

I am aware, but the API this is being created for uses CamelCase for their properties (in JSON). I thought it would be less confusing to keep that consistent, and also so I don't have to convert/swap between the two.

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