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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 get_data_path(self, filename, env_prefix=None):
 """ Get data path. Args: filename (string) : Name of file inside of /data folder to retrieve. Kwargs: env_prefix (string) : Name of subfolder, ex: 'qa' will find files in /data/qa Returns: String - path to file. Usage:: open(WTF_DATA_MANAGER.get_data_path('testdata.csv') Note: WTF_DATA_MANAGER is a provided global instance of DataManager """

        if env_prefix == None:
            target_file = filename
        else:
            target_file = os.path.join(env_prefix, filename)

        if os.path.exists(os.path.join(self._data_path, target_file)):
            return os.path.join(self._data_path, target_file)
        else:
            raise DataNotFoundError(
                u("Cannot find data file: {0}").format(target_file))