find_path.py

data = [('SFO', 'HKO'), ('YYZ', 'SFO'), ('YUL', 'YYZ'), ('HKO', 'ORD')]

# extract nodes
nodes = list(set([val for s in data for val in s]))

# build a graph
graph = {}
for n in nodes:
    graph[n] = []
    paths = [path for path in data if n in path]
    connections = list(set([val for s in paths for val in s]))
    connections.remove(n)
    graph[n] = connections


# function to be called recursively to find a path from a point to another.
def find_path(graph, start, end, path=[]):
    path = path + [start]
    if start == end:
        return path
    if not graph.has_key(start):
        return None
    for node in graph[start]:
        if node not in path:
            new_path = find_path(graph, node, end, path)
            if new_path: return new_path
    return None


all_paths = []
for n in nodes:
    path = find_path(graph=graph, start='SFO', end=n)
    all_paths.append(path)
    
print(all_paths)