mementum

class MyMFIStrategy(bt.Strategy):
    def __init__(self):
        mfi = bt.MFI_Canonical(self.data)

mementum

class MFI_Canonical(bt.Indicator):
    lines = ('mfi',)
    params = dict(period=14)

    def __init__(self):
        psum = self.data.close + self.data.low + self.data.high
        tprice = psum / 3.0
        mfraw = tprice * self.data.volume
        ...