updates

train.py

@@ -204,8 +204,7 @@ def train():
     model.nc = nc  # attach number of classes to model
     model.arc = opt.arc  # attach yolo architecture
     model.hyp = hyp  # attach hyperparameters to model
-    if hasattr(dataset, 'labels'):
-        model.class_weights = labels_to_class_weights(dataset.labels, nc).to(device)  # attach class weights
+    model.class_weights = labels_to_class_weights(dataset.labels, nc).to(device)  # attach class weights
     torch_utils.model_info(model, report='summary')  # 'full' or 'summary'
     nb = len(dataloader)
     maps = np.zeros(nc)  # mAP per class

utils/utils.py

@@ -43,14 +43,16 @@ def load_classes(path):
 
 def labels_to_class_weights(labels, nc=80):
     # Get class weights (inverse frequency) from training labels
-    ni = len(labels)  # number of images
+    if labels[0] is None:  # no labels loaded
+        return None
+
     labels = np.concatenate(labels, 0)  # labels.shape = (866643, 5) for COCO
     classes = labels[:, 0].astype(np.int)  # labels = [class xywh]
     weights = np.bincount(classes, minlength=nc)  # occurences per class
 
     # Prepend gridpoint count (for uCE trianing)
     # gpi = ((320 / 32 * np.array([1, 2, 4])) ** 2 * 3).sum()  # gridpoints per image
-    # weights = np.hstack([gpi * ni - weights.sum() * 9, weights * 9]) ** 0.5  # prepend gridpoints to start
+    # weights = np.hstack([gpi * len(labels)  - weights.sum() * 9, weights * 9]) ** 0.5  # prepend gridpoints to start
 
     weights[weights == 0] = 1  # replace empty bins with 1
     weights = 1 / weights  # number of targets per class