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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 read_files(*filenames):
 """ Output the contents of one or more files to a single concatenated string. """

    output = []
    for filename in filenames:
        f = codecs.open(filename, encoding='utf-8')
        try:
            output.append(f.read())
        finally:
            f.close()
    return '\n\n'.join(output)