ultralytics 8.0.136 refactor and simplify package (#3748)

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/utils/callbacks/tensorboard.py

@@ -0,0 +1,47 @@
+# Ultralytics YOLO 🚀, AGPL-3.0 license
+
+from ultralytics.utils import LOGGER, TESTS_RUNNING, colorstr
+
+try:
+    from torch.utils.tensorboard import SummaryWriter
+
+    assert not TESTS_RUNNING  # do not log pytest
+except (ImportError, AssertionError):
+    SummaryWriter = None
+
+writer = None  # TensorBoard SummaryWriter instance
+
+
+def _log_scalars(scalars, step=0):
+    """Logs scalar values to TensorBoard."""
+    if writer:
+        for k, v in scalars.items():
+            writer.add_scalar(k, v, step)
+
+
+def on_pretrain_routine_start(trainer):
+    """Initialize TensorBoard logging with SummaryWriter."""
+    if SummaryWriter:
+        try:
+            global writer
+            writer = SummaryWriter(str(trainer.save_dir))
+            prefix = colorstr('TensorBoard: ')
+            LOGGER.info(f"{prefix}Start with 'tensorboard --logdir {trainer.save_dir}', view at http://localhost:6006/")
+        except Exception as e:
+            LOGGER.warning(f'WARNING ⚠️ TensorBoard not initialized correctly, not logging this run. {e}')
+
+
+def on_batch_end(trainer):
+    """Logs scalar statistics at the end of a training batch."""
+    _log_scalars(trainer.label_loss_items(trainer.tloss, prefix='train'), trainer.epoch + 1)
+
+
+def on_fit_epoch_end(trainer):
+    """Logs epoch metrics at end of training epoch."""
+    _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}