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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 file_prepender(filename):
 """ Prepend an informational header on files managed by Molecule and returns None. :param filename: A string containing the target filename. :return: None """

    with open_file(filename, 'r+') as f:
        content = f.read()
        f.seek(0, 0)
        f.write(molecule_prepender(content))