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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 _set_global_vars(metadata):
 """Identify files used multiple times in metadata and replace with global variables """

    fnames = collections.defaultdict(list)
    for sample in metadata.keys():
        for k, v in metadata[sample].items():
            if isinstance(v, six.string_types) and os.path.isfile(v):
                v = _expand_file(v)
                metadata[sample][k] = v
                fnames[v].append(k)
    global_vars = {}
    # Skip global vars -- more confusing than useful
    # loc_counts = collections.defaultdict(int)
    # global_var_sub = {}
    # for fname, locs in fnames.items():
    #     if len(locs) > 1:
    #         loc_counts[locs[0]] += 1
    #         name = "%s%s" % (locs[0], loc_counts[locs[0]])
    #         global_var_sub[fname] = name
    #         global_vars[name] = fname
    # for sample in metadata.keys():
    #     for k, v in metadata[sample].items():
    #         if isinstance(v, six.string_types) and v in global_var_sub:
    #             metadata[sample][k] = global_var_sub[v]
    return metadata, global_vars