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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 replace_version_string(content, variable, new_version):
 """ Given the content of a file, finds the version string and updates it. :param content: The file contents :param variable: The version variable name as a string :param new_version: The new version number as a string :return: A string with the updated version number """

    return re.sub(
        r'({0} ?= ?["\'])\d+\.\d+(?:\.\d+)?(["\'])'.format(variable),
        r'\g<1>{0}\g<2>'.format(new_version),
        content
    )