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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 merge_required_files(dirnames, out_dir):
 """Merges the required files from each of the directories. :param dirnames: the list of directories to merge data from. :param out_dir: the name of the output directory. :type dirnames: list :type out_dir: str """

    # The list of files to merge
    fn_to_merge = ("steps_summary.tex", "excluded_markers.txt",
                   "excluded_samples.txt")

    # Merging the files
    for fn in fn_to_merge:
        o_fn = os.path.join(out_dir, fn)
        with open(o_fn, "w") as o_file:
            for dn in dirnames:
                i_fn = os.path.join(dn, fn)
                with open(i_fn, "r") as i_file:
                    o_file.write(i_file.read())

    # Merging the result summary file
    o_fn = os.path.join(out_dir, "results_summary.txt")
    with open(o_fn, "w") as o_file:
        for i, dn in enumerate(dirnames):
            i_fn = os.path.join(dn, "results_summary.txt")
            with open(i_fn, "r") as i_file:
                if i != 0:
                    # We skip the first 4 lines (file descriptions)
                    [i_file.readline() for i in range(4)]
                o_file.write(i_file.read())

    # Merging the graphic paths file
    graphic_paths = set()
    for dn in dirnames:
        fn = os.path.join(dn, "graphic_paths.txt")
        if os.path.isfile(fn):
            with open(fn, "r") as i_file:
                graphic_paths.update({
                    os.path.join(dn, path)
                    for path in i_file.read().splitlines()
                })
    if len(graphic_paths) > 0:
        with open(os.path.join(out_dir, "graphic_paths.txt"), "w") as o_file:
            for path in sorted(graphic_paths):
                print >>o_file, os.path.relpath(path, out_dir)