How to write __init__() in customized Commission schema?

soulmachine

I've written a customized commission schema that supports fractional size:

class CryptoCommissionInfo(bt.CommissionInfo):
    '''Commission scheme for cryptocurrency spot market.'''
    params = (
        ('stocklike', True),
        ('commtype', bt.CommInfoBase.COMM_PERC), # apply % commission
    )
    
    def __init__(self, commission: float = None):
        assert abs(commission) < 1.0 # commission is a percentage, error: bad operand type for abs(): 'NoneType'
        super().__init__()

    def getsize(self, price, cash):
        '''Support fractional-size.
        
            More details at https://www.backtrader.com/blog/posts/2019-08-29-fractional-sizes/fractional-sizes/.
        '''
        return self.p.leverage * (cash / price)

Everything works fine except the code in __init__().

I think this is related to meta programming in Python, which I'm not familiar with.

Can someone fix my __init__() function? Thanks!

vladisld

@soulmachine said in How to write __init__() in customized Commission schema?:

def init(self, commission: float = None):

Please try to remove the commission argument from the __init__ method. The commission is defined as one of params (in CommInfoBase) and will be processed by MetaParams metaclass (as you've correctly mentioned):

def __init__(self):
        assert abs(self.p.commission) < 1.0 # commission is a percentage, error: bad operand type for abs(): 'NoneType'
        super().__init__()

soulmachine

@vladisld Thanks, it works! I shared my complete code in another post https://community.backtrader.com/topic/2806/share-my-customized-commission-scheme-for-cryptocurrencies