I have made a package called resolvepy which solves homogenous recurrence relations. After downloading, you can solve a reccurrence relation like this:

from sympy import *
from resolvepy import *

n = Symbol('n')

# create the sequence
f = Recurrence('f')
f.index = n

# input the starting items
f[0] = 1
f[1] = 2

# provide a recursive formula
f[n] = f[n-1] + f[n-2]

explicit = f.resolve()