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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 tqdm(self):
 """Add a progression bar for the current download."""

    async_tqdm = utils.async_tqdm
    with async_tqdm(total=0, desc='Dl Completed...', unit=' url') as pbar_url:
      with async_tqdm(total=0, desc='Dl Size...', unit=' MiB') as pbar_dl_size:
        self._pbar_url = pbar_url
        self._pbar_dl_size = pbar_dl_size
        yield