Expr.coeff 的文档字符串,它会提到In addition, no factoring is done, so 1 + z*(1 + y) is not obtained from the following: >>> (x + z*(x + x*y)).coeff(x) 1 因此,它实际上是在检查表达式所写的中的项的因子以获取感兴趣的因子。