import networkx as nx
def crea_xarxa_metro(nomf='metrobcn.txt'):
    g = nx.Graph()
    with open(nomf, 'r') as f:
        parades = []
        for lin in f:
            lin = lin.strip()
            if lin[0] == '=':
                nx.add_path(g, parades, linia=lin[1:])
                parades = []
            else:
                parades.append(lin)
    return g