sy.sympify(str(expression))不等于expression

据我所知, str 将sympy表达式转换为字符串并 sympify 将字符串转换为sympy表达式。因此,我希望(对于合理的表达方式)如下。

>>> sy.sympify(str(expr)) == expr
True

我试过这个,事实上这是简单的例子(例如, expr = x+y )。但是,当我用下面的表达式尝试时,它不起作用:

import sympy as sy
a = sy.symbols("a")
A = sy.Matrix(3,3, a)
c0,c1,c2 = sy.symbols("c0 c1 c2", positive = True)
c1*c2**2*a(0, 1)**2*a(1, 2)*a(2, 2) - c1*c2**2*a(0, 1)**2*a(2, 2)**2 - c1*c2**2*a(0, 1)*a(0, 2)*a(1, 1)*a(2, 2) + c1*c2**2*a(0, 1)*a(0, 2)*a(2, 1)*a(2, 2) - c1*c2**2*a(0, 1)*a(1, 1)*a(1, 2)*a(2, 2) + c1*c2**2*a(0, 1)*a(1, 1)*a(2, 2)**2 + c1*c2**2*a(0, 2)*a(1, 1)**2*a(2, 2) - c1*c2**2*a(0, 2)*a(1, 1)*a(2, 1)*a(2, 2) - c1*a(0, 0)**2*a(1, 1)*a(2, 1) + c1*a(0, 0)**2*a(2, 1)**2 + c1*a(0, 0)*a(0, 1)*a(1, 1)*a(2, 0) - c1*a(0, 0)*a(0, 1)*a(2, 0)*a(2, 1) + c1*a(0, 0)*a(1, 0)*a(1, 1)*a(2, 1) - c1*a(0, 0)*a(1, 0)*a(2, 1)**2 - c1*a(0, 0)*a(1, 1)**2*a(2, 0) + c1*a(0, 0)*a(1, 1)*a(2, 0)*a(2, 1) - c2**2*a(0, 0)*a(0, 1)*a(1, 2)*a(2, 2) + c2**2*a(0, 0)*a(0, 1)*a(2, 2)**2 + c2**2*a(0, 0)*a(0, 2)*a(1, 1)*a(2, 2) - c2**2*a(0, 0)*a(0, 2)*a(2, 1)*a(2, 2) + c2**2*a(0, 1)*a(1, 0)*a(1, 2)*a(2, 2) - c2**2*a(0, 1)*a(1, 0)*a(2, 2)**2 - c2**2*a(0, 2)*a(1, 0)*a(1, 1)*a(2, 2) + c2**2*a(0, 2)*a(1, 0)*a(2, 1)*a(2, 2) + c2*a(0, 0)**2*a(1, 2)*a(2, 1) - c2*a(0, 0)**2*a(2, 1)*a(2, 2) - c2*a(0, 0)*a(0, 1)*a(1, 2)*a(2, 0) + c2*a(0, 0)*a(0, 1)*a(2, 0)*a(2, 2) - c2*a(0, 0)*a(1, 0)*a(1, 2)*a(2, 1) + c2*a(0, 0)*a(1, 0)*a(2, 1)*a(2, 2) + c2*a(0, 0)*a(1, 1)*a(1, 2)*a(2, 0) - c2*a(0, 0)*a(1, 1)*a(2, 0)*a(2, 2)

有人能告诉我为什么这个表达不起作用吗?

注:我知道我应该举一个最简单的例子,但我只是没有找到表达式的哪个部分导致了这个问题。