def edge_frequency_dictionary(edges, freq = {}):
    """
    Augments counters within graph G edges based on if they're contained within the edges list.

    Parameters
    ----------
    edges : list
        list of edge tuples in the format (start node, end node, 0)
    freq : dictionary
        dictionary of frequencies, with edge tuples as keys in the
        format (start node, end node, 0) and frequency as integer values
        defaults to empty dictionary

    Returns
    -------
    frequency : dictionary
        dictionary of frequencies, with edge tuples as keys in the
        format (start node, end node, 0) and frequency as integer values
    """
    # iterate over edges, with each edge as a key
    for key in edges:
        if key in freq:
            freq[key] += 1
        else:
            freq[key] = 1
    return freq