[Solved] Nested list doesn’t work properly

I think the problem is the assignment equation = eqn. Since eqn is a list, it is a mutable and thus passed as a reference, when you assign a mutable, the variable actually contains a pointer to that object. This means that equation and eqn are the same list.

You should

from copy import deepcopy
equation = deepcopy(eqn)

You need deepcopy instead of copy because you have a list of lists, also the inner list needs to be copied.