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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 set_asset_dir(self):
 """Returns the ASSET_DIR environment variable This method gets the ASSET_DIR environment variable for the current asset install. It returns either the string value if set or None if it is not set. :return: None """

        log = logging.getLogger(self.cls_logger + '.get_asset_dir')
        try:
            self.asset_dir = os.environ['ASSET_DIR']
        except KeyError:
            log.warn('Environment variable ASSET_DIR is not set!')
        else:
            log.info('Found environment variable ASSET_DIR: {a}'.format(a=self.asset_dir))