Fix TypeError: 'PosixPath' object is not iterable (#3285)

train.py

@@ -419,7 +419,7 @@ def train(hyp, opt, device, tb_writer=None):
         # Test best.pt
         logger.info('%g epochs completed in %.3f hours.\n' % (epoch - start_epoch + 1, (time.time() - t0) / 3600))
         if opt.data.endswith('coco.yaml') and nc == 80:  # if COCO
-            for m in (last, best) if best.exists() else (last):  # speed, mAP tests
+            for m in [last, best] if best.exists() else [last]:  # speed, mAP tests
                 results, _, _ = test.test(opt.data,
                                           batch_size=batch_size * 2,
                                           imgsz=imgsz_test,