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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 save(filepath=None, **kwargs):
 """ Saves a list of keyword arguments as environment variables to a file. If no filepath given will default to the default `.env` file. """

    if filepath is None:
        filepath = os.path.join('.env')

    with open(filepath, 'wb') as file_handle:
        file_handle.writelines(
            '{0}={1}\n'.format(key.upper(), val)
            for key, val in kwargs.items()
        )