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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 preload_tops(meta):
 """Load all topology files into memory. This might save some performance compared to re-parsing the topology file for each trajectory you try to load in. Typically, you have far fewer (possibly 1) topologies than trajectories Parameters meta : pd.DataFrame The DataFrame of metadata with a column named 'top_fn' Returns ------- tops : dict Dictionary of ``md.Topology`` objects, keyed by "top_fn" values. """

    top_fns = set(meta['top_fn'])
    tops = {}
    for tfn in top_fns:
        tops[tfn] = md.load_topology(tfn)
    return tops