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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 add_pythonpath(path):
 """ Prepend given path to environment variable PYTHONPATH. :param path: Path to add to PYTHONPATH. :return: New PYTHONPATH value. """

    # Get PYTHONPATH value. Default is empty string.
    pythonpath = os.environ.setdefault('PYTHONPATH', '')

    # If given path is not in PYTHONPATH
    if path not in pythonpath.split(os.pathsep):
        # Prepend given path to PYTHONPATH
        pythonpath = os.environ['PYTHONPATH'] = \
            (path + os.pathsep + pythonpath) if pythonpath else path

    # Return new PYTHONPATH value
    return pythonpath