<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_collection(self, lang=None, task=None):
 """ Return the collection that represents a specific language or task. Args: lang (string):
 Language code. task (string):
 Task name. """

    if lang: id = "{}{}".format(Downloader.LANG_PREFIX, lang)
    elif task: id = "{}{}".format(Downloader.TASK_PREFIX, task)
    else: raise ValueError("You should pass either the task or the lang")
    try:
      return self.info(id)
    except ValueError as e:
      if lang: raise LanguageNotSupported("Language {} is not supported".format(id))
      if task: raise TaskNotSupported("Task {} is not supported".format(id))