HUB setup (#108)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/yolo/utils/callbacks/tensorboard.py

@@ -0,0 +1,27 @@
+from torch.utils.tensorboard import SummaryWriter
+
+writer = None  # TensorBoard SummaryWriter instance
+
+
+def _log_scalars(scalars, step=0):
+    for k, v in scalars.items():
+        writer.add_scalar(k, v, step)
+
+
+def on_pretrain_routine_start(trainer):
+    global writer
+    writer = SummaryWriter(str(trainer.save_dir))
+
+
+def on_batch_end(trainer):
+    _log_scalars(trainer.label_loss_items(trainer.tloss, prefix="train"), trainer.epoch + 1)
+
+
+def on_fit_epoch_end(trainer):
+    _log_scalars(trainer.metrics, trainer.epoch + 1)
+
+
+callbacks = {
+    "on_pretrain_routine_start": on_pretrain_routine_start,
+    "on_fit_epoch_end": on_fit_epoch_end,
+    "on_batch_end": on_batch_end}