def tax_subtract(price, tax_percentage=21):
    if price is None:
        return None

    result = price / ((100 + tax_percentage) / D(100))
    return result.quantize(D('0.01'), ROUND_HALF_UP)
Subtract the given `tax_percentage` from the given `price`.
dataset/ETHPy150Open django-oscar/django-oscar/src/oscar/test/factories/utils.py/tax_subtract