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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 get_context_files(data):
 """Retrieve pre-installed annotation files for annotating genome context. """

    ref_file = dd.get_ref_file(data)
    all_files = []
    for ext in [".bed.gz"]:
        all_files += sorted(glob.glob(os.path.normpath(os.path.join(os.path.dirname(ref_file), os.pardir,
                                                                    "coverage", "problem_regions", "*",
                                                                    "*%s" % ext))))
    return sorted(all_files)