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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 _edge_list_to_dataframe(ls, src_column_name, dst_column_name):
 """ Convert a list of edges into dataframe. """

    assert HAS_PANDAS, 'Cannot use dataframe because Pandas is not available or version is too low.'
    cols = reduce(set.union, (set(e.attr.keys()) for e in ls))
    df = pd.DataFrame({
        src_column_name: [e.src_vid for e in ls],
        dst_column_name: [e.dst_vid for e in ls]})
    for c in cols:
        df[c] = [e.attr.get(c) for e in ls]
    return df