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# Source code for fnss.netconfig.weights

    """
    Provides functions to assign and manipulate link weights to a network topology.
    """
    import networkx as nx

    __all__ = [
        'set_weights_inverse_capacity',
        'set_weights_constant',
        'set_weights_delays',
        'get_weights',
        'clear_weights'
               ]

    def set_weights_inverse_capacity(topology):
        """
        Assign link weights to links proportionally to the inverse of their
        capacity. Weights are normalized so that the minimum weight is 1.

        Parameters
        ----------
        topology : Topology
            The topology on which weights are applied.

        Examples
        --------
        >>> import fnss
        >>> topology = fnss.Topology()
        >>> topology.add_path([1,2,3,4])
        >>> fnss.set_capacities_constant(topology, 10, 'Mbps')
        >>> fnss.set_weights_inverse_capacity(topology)
        """
        try:
            max_capacity = float(max((topology.edge[u][v]['capacity']
                                      for u, v in topology.edges_iter())))
        except KeyError:
            raise ValueError('All links must have a capacity attribute')
        for u, v in topology.edges_iter():
            capacity = topology.edge[u][v]['capacity']
            weight = max_capacity/capacity
            topology.edge[u][v]['weight'] = weight

    def set_weights_delays(topology):
        """
        Assign link weights to links proportionally their delay. Weights are
        normalized so that the minimum weight is 1.

        Parameters
        ----------
        topology : Topology
            The topology on which weights are applied.

        Examples
        --------
        >>> import fnss
        >>> topology = fnss.erdos_renyi_topology(50, 0.1)
        >>> fnss.set_delays_constant(topology, 2, 'ms')
        >>> fnss.set_weights_delays(topology)

        """
        try:
            min_delay = float(min((topology.edge[u][v]['delay']
                                   for u, v in topology.edges_iter())))
        except KeyError:
            raise ValueError('All links must have a delay attribute')
        for u, v in topology.edges_iter():
            delay = topology.edge[u][v]['delay']
            weight = delay / min_delay
            topology.edge[u][v]['weight'] = weight

    def set_weights_constant(topology, weight=1.0, links=None):
        """
        Assign a constant weight to all selected links

        Parameters
        ----------
        topology : Topology
            The topology on which weights are applied.
        weight : float, optional
            The constant weight to be applied to all links
        links : iterable, optional
            Iterable container of selected links on which weights are applied.
            If it is None, all links are selected

        Examples
        --------
        >>> import fnss
        >>> topology = fnss.Topology()
        >>> topology.add_edges_from([(1, 2), (5, 8), (4, 5), (1, 7)])
        >>> fnss.set_weights_constant(topology, weight=1.0, links=[(1, 2), (5, 8), (4, 5)])
        """
        edges = topology.edges_iter() if links is None else links
        for u, v in edges:
            topology.edge[u][v]['weight'] = weight

    def get_weights(topology):
        """
        Returns all the weights.

        Parameters
        ----------
        topology : Topology

        Returns
        -------
        weights : dict
            Dictionary of weights keyed by link.

        Examples
        --------
        >>> import fnss
        >>> topology = fnss.Topology()
        >>> topology.add_path([1, 2, 3])
        >>> fnss.set_weights_constant(topology, weight=2.0)
        >>> weight = fnss.get_weights(topology)
        >>> weight[(1,2)]
        2.0
        """
        return nx.get_edge_attributes(topology, 'weight')

    def clear_weights(topology):
        """
        Remove all weights from the topology.

        Parameters
        ----------
        topology : Topology
        """
        for u, v in topology.edges_iter():
            if 'weight' in topology.edge[u][v]:
                del topology.edge[u][v]['weight']

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