def __rmatmul__(self, other):
    if isinstance(other, Observable):
        self.obs[:0] = [other]
        return self
    raise ValueError('Can only perform tensor products between observables.')
def __rmatmul__(self, other):
    if isinstance(other, Observable):
        self.obs[:0] = [other]
        return self
    raise ValueError('Can only perform tensor products between observables.')