Python: how to use attribute from differenct class

Question

I have some basic class Trader in trader.py:

class Trader(object):
    def __init__(self, exchange_name, api_key, api_secret):
        self.Exchange = Exchange(exchange_name, api_key, api_secret).exchange

and a class Exchange in exchange.py

class Exchange(object):
    def __init__(self, name, api_key, api_secret):
        self.name = name
        exchange_id = name
        exchange_class = getattr(ccxt, exchange_id)
        self.exchange = exchange_class({
            'apiKey': api_key,
            'secret': api_secret,
            'timeout': 30000,
            'enableRateLimit': True,
        })

The above works. So I can use self.Exchange inside the Trader class to use functions against the exchange. But it works only because of this line:

self.Exchange = Exchange(exchange_name, api_key, api_secret).exchange

I don't like the fact I have to put .exchange after it. I'm just a bit playing and learning python. I'm not very experienced in python programming / I'm also not a coin trader, but I liked the ccxt package.

How can I make this work without needing to putting the .exchange behind my Exchange(...) or is this normal behaviour? Or do I have to make my exchange class in a different way?

Thanks

Answer 1

Since exchange is an attribute of an instance of the Exchange class, this is normal behavior.

If you want to access exchange without needing to put .exchange after your Exchange object, you might consider doing away with the Exchange class entirely—since it seems you only use it to get the instance of the exchange_class from ccxt—and writing a function instead.

Here's an example:

def get_exchange(exchange_name, api_key, api_secret):
    exchange_class = getattr(ccxt, exchange_id)
    return exchange_class({
        'apiKey': api_key,
        'secret': api_secret,
        'timeout': 30000,
        'enableRateLimit': True,
    })

class Trader:
    def __init__(self, exchange_name, api_key, api_secret):
        self.exchange = get_exchange(exchange_name, api_key, api_secret)

This way an exchange will be accessible directly by instances of Trader.