Python-сообщество

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import time
graph = {'begin': {'L1'},
         'L1'   : {'BL2'},
         'BL2' :  {'L2', 'EL2'},
         'L2'   : {'EL2'},
         'EL2' :  {'BL5'},
         }
n = 20
for i in range(3,n):
    graph['EL'+str(i-1)] = {'BL'+str(i)}
    graph['BL'+str(i)] = {'EL'+str(i), 'L'+str(i)}
    graph['L'+str(i)] = {'EL'+str(i)}
    if i == n-1:
        graph['EL'+str(i)] = {'end'}
def dfs_paths(graph, start, goal):
    stack = [(start, [start])]
    while stack:
        (vertex, path) = stack.pop()
        for next in graph[vertex] - set(path):
            if next == goal:
                yield path + [next]
            else:
                stack.append((next, path + [next]))
begin = time.time()
print u'Обход всех путей...'
for path in dfs_paths(graph, 'begin', 'end'):
    pass
print u'Обход завершён...'
end = time.time()
print end-begin