'Check whether conversion is possible from *fromty* to *toty*.
If successful, return a numba.typeconv.Conversion instance;
otherwise None is returned.'

def can_convert(self, fromty, toty):

    if (fromty == toty):
        return Conversion.exact
    else:
        conv = self.tm.check_compatible(fromty, toty)
        if (conv is not None):
            return conv
        forward = fromty.can_convert_to(self, toty)
        backward = toty.can_convert_from(self, fromty)
        if (backward is None):
            return forward
        elif (forward is None):
            return backward
        else:
            return min(forward, backward)
