Add ndjson logging for training (#10970)

* Add ndjson logging for training

This adds support for NDJSON (newline-delimited JSON) metrics logging,
for both console (stdout) output and a file (like the current CSV file).

NDJSON can be easily grepped from the output and/or parsed with e.g. `jq`.

The feature is enabled with the `--ndjson-console` and `--ndjson-file`
switches to `train.py`.

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---------

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

train.py

@@ -58,7 +58,7 @@ from utils.general import (LOGGER, TQDM_BAR_FORMAT, check_amp, check_dataset, ch
                            get_latest_run, increment_path, init_seeds, intersect_dicts, labels_to_class_weights,
                            labels_to_image_weights, methods, one_cycle, print_args, print_mutation, strip_optimizer,
                            yaml_save)
-from utils.loggers import Loggers
+from utils.loggers import LOGGERS, Loggers
 from utils.loggers.comet.comet_utils import check_comet_resume
 from utils.loss import ComputeLoss
 from utils.metrics import fitness
@@ -98,7 +98,20 @@ def train(hyp, opt, device, callbacks):  # hyp is path/to/hyp.yaml or hyp dictio
     # Loggers
     data_dict = None
     if RANK in {-1, 0}:
-        loggers = Loggers(save_dir, weights, opt, hyp, LOGGER)  # loggers instance
+        include_loggers = list(LOGGERS)
+        if getattr(opt, 'ndjson_console', False):
+            include_loggers.append('ndjson_console')
+        if getattr(opt, 'ndjson_file', False):
+            include_loggers.append('ndjson_file')
+
+        loggers = Loggers(
+            save_dir=save_dir,
+            weights=weights,
+            opt=opt,
+            hyp=hyp,
+            logger=LOGGER,
+            include=tuple(include_loggers),
+        )
 
         # Register actions
         for k in methods(loggers):
@@ -482,6 +495,10 @@ def parse_opt(known=False):
     parser.add_argument('--bbox_interval', type=int, default=-1, help='Set bounding-box image logging interval')
     parser.add_argument('--artifact_alias', type=str, default='latest', help='Version of dataset artifact to use')
 
+    # NDJSON logging
+    parser.add_argument('--ndjson-console', action='store_true', help='Log ndjson to console')
+    parser.add_argument('--ndjson-file', action='store_true', help='Log ndjson to file')
+
     return parser.parse_known_args()[0] if known else parser.parse_args()