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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def pegasus_layout(G, scale=1., center=None, dim=2, crosses=False):
 """Positions the nodes of graph G in a Pegasus topology. NumPy (http://scipy.org) is required for this function. Parameters G : NetworkX graph Should be a Pegasus graph or a subgraph of a Pegasus graph. This should be the product of dwave_networkx.pegasus_graph scale : float (default 1.) Scale factor. When scale = 1, all positions fit within [0, 1] on the x-axis and [-1, 0] on the y-axis. center : None or array (default None) Coordinates of the top left corner. dim : int (default 2) Number of dimensions. When dim > 2, all extra dimensions are set to 0. crosses: boolean (optional, default False) If crosses is True, K_4,4 subgraphs are shown in a cross rather than L configuration. Ignored if G was defined with nice_coordinates=True. Returns ------- pos : dict A dictionary of positions keyed by node. Examples -------- """


    if not isinstance(G, nx.Graph) or G.graph.get("family") != "pegasus":
        raise ValueError("G must be generated by dwave_networkx.pegasus_graph")

    if G.graph.get('labels') == 'nice':
        m = 3*(G.graph['rows']-1)
        c_coords = chimera_node_placer_2d(m, m, 4, scale=scale, center=center, dim=dim)
        def xy_coords(t, y, x, u, k): return c_coords(3*y+2-t, 3*x+t, u, k)
        pos = {v: xy_coords(*v) for v in G.nodes()}
    else:
        xy_coords = pegasus_node_placer_2d(G, scale, center, dim, crosses=crosses)

        if G.graph.get('labels') == 'coordinate':
            pos = {v: xy_coords(*v) for v in G.nodes()}
        elif G.graph.get('data'):
            pos = {v: xy_coords(*dat['pegasus_index']) for v, dat in G.nodes(data=True)}
        else:
            m = G.graph.get('rows')
            coord = pegasus_coordinates(m)
            pos = {v: xy_coords(*coord.tuple(v)) for v in G.nodes()}

    return pos