class instantiation gives positional error in python

Question

i have a class definition as follows :

class Trade:
  def __init__(self, **kwargs):
    # lots of things

I am trying to instantiate one by doing :

trade_tmp = Trade(json.loads(trade_str))

My understanding was that the **kwargs argument would automatically pickup the generated dictionary. Am I incorrect ?

I am getting the whole takes 1 positional argument but 2 were given error which I though should not apply here.

Answer 1

The dict returned by json.loads serves as a single argument to the function. Therefore you need another positional argument:

def __init__(self, data, **kwargs)

While you could prepend two starts before the dict to force it as keyword arguments, it's not designed for this purpose and I recommend against this:

# it's valid, but don't do this
Trade(**json.loads(trade_str))

Answer 2

Two choices, using args or kwargs:

import json

class Trade1:
  def __init__(self, **kwargs):
      print(kwargs)

class Trade2:
  def __init__(self, *args):
      print(args)

trade_str = '{"a": 1, "b": 2}'
trade_tmp1 = Trade1(**json.loads(trade_str))
trade_tmp2 = Trade2(json.loads(trade_str))