def imageset(self, imageset = "trainval"):
        imageset = "{0}.txt".format(imageset)
        path = os.path.join(self.root, "ImageSets", "Main", imageset)
        for line in open(path):
            yield line.strip()
imageset should be: trainval, train, or val
dataset/ETHPy150Open cvondrick/pyvision/vision/pascal.py/PascalDataset.imageset