Sort a sum of products in sympy output-CodePudding

I try to find a pattern using simpy.

import numpy as np
import sympy
from sympy import *
from sympy import simplify

b = symbols('b:100')
a = symbols('a:100')


A = Matrix([[1, 0],[0, 1]])
for i in [10,9,8]:
        A = A @ Matrix([[1 b[i]-a[i] , -b[i]],[1, 0]])

print(expand(simplify(A[0,0])))

The output is

-a10*a8*a9   a10*a8*b9   a10*a8   a10*a9*b8   a10*a9 - a10*b8*b9 - a10*b8 - a10   a8*a9*b10   a8*a9 - a8*b10*b9 - a8*b9 - a8 - a9*b10*b8 - a9*b10 - a9*b8 - a9   b10*b8*b9   b8*b9   b8   1

Is there any way to sort the summands in a more usefull way? Like show first all summands with containing 3 characters and then summands with only 2 ... and also sort the products in the summands so that a comes before b and a10 before a9 before a8 and so on?

theres a command "sorted" in the simpy bib but i need list elements for this command. Any other nice suggestions to solve this problem?

CodePudding user response：

You can make your own key when sorting. Does this do what you want?