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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 getDatabaseFileSize(self):
 """ Return the file size of the database as a pretty string. """

    if DISABLE_PERSISTENT_CACHING:
      return "?"
    size = os.path.getsize(self.__db_filepath)
    if size > 1000000000:
      size = "%0.3fGB" % (size / 1000000000)
    elif size > 1000000:
      size = "%0.2fMB" % (size / 1000000)
    elif size > 1000:
      size = "%uKB" % (size // 1000)
    else:
      size = "%uB" % (size)
    return size