Draw shape without picking up pen

draw.py

#!/usr/bin/env python3

import copy
import sys

lines = {
        1:[2,3],
        2:[1,3,4,6,7],
        3:[1,2,5,6,7],
        4:[2,5,6,7],
        5:[3,7],
        6:[2,3,4,7,8],
        7:[2,3,5,6,8],
        8:[6,7]
    }

def check(cstate):
        
    if len(cstate) != 8:
        return
    for offset in lines:
        if sorted(lines[offset]) != sorted(cstate[offset]):
            return
    print("Solution!")
    sys.exit()

def iteration(clocation, cstate):

    print("iteration(%s %s)" % (clocation, cstate))

    check(cstate)

    for ilocation in lines[clocation]:
        print("%d -> %d" % (clocation, ilocation))
        nstate = copy.deepcopy(cstate)
        y = nstate.get(clocation, [])
        x = nstate.get(ilocation, [])

        if ilocation in y:
            continue

        y = y + [ilocation]
        x = x + [clocation]

        nstate[clocation] = y
        nstate[ilocation] = x
        iteration(ilocation, nstate)

iteration(1, {})
iteration(2, {})