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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 _dataframe_to_edge_list(df):
 """ Convert dataframe into list of edges, assuming that source and target ids are stored in _SRC_VID_COLUMN, and _DST_VID_COLUMN respectively. """

    cols = df.columns
    if len(cols):
        assert _SRC_VID_COLUMN in cols, "Vertex DataFrame must contain column %s" % _SRC_VID_COLUMN
        assert _DST_VID_COLUMN in cols, "Vertex DataFrame must contain column %s" % _DST_VID_COLUMN
        df = df[cols].T
        ret = [Edge(None, None, _series=df[col]) for col in df]
        return ret
    else:
        return []