import sympy as sp
x, y, z, w = sp.symbols('x, y, z, w')
rho, sigma, beta = sp.symbols('rho, sigma, beta')
z = w
f1 = sigma * (y - x)
f2 = x * (rho - z) - y
f3 = x * y - beta * w
f4 = z - w
print(sp.solvers.solve((f1, f2, f3, f4), (x, y, z, w)))
Решение системы уравнений с Sympy, python2.7