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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 _image_loop(self):
 """Retrieve an iterable of images either with, or without a progress bar."""

        if self.progress_bar and 'tqdm' in self.progress_bar.lower():
            return tqdm(self.imgs, desc='Saving PNGs as flat PDFs', total=len(self.imgs), unit='PDFs')
        else:
            return self.imgs