chore: import upstream snapshot with attribution

python/ray/train/v2/_internal/callbacks/env_callback.py

@@ -0,0 +1,39 @@
+import importlib
+import os
+from typing import List
+
+from ray.train.v2._internal.constants import RAY_TRAIN_CALLBACKS_ENV_VAR
+from ray.train.v2._internal.execution.callback import RayTrainCallback
+
+
+def _initialize_env_callbacks() -> List[RayTrainCallback]:
+    """Initialize callbacks from environment variable.
+
+    Returns:
+        List of callbacks initialized from environment variable.
+    """
+    callbacks = []
+    callbacks_str = os.environ.get(RAY_TRAIN_CALLBACKS_ENV_VAR, "")
+    if not callbacks_str:
+        return callbacks
+
+    for callback_path in callbacks_str.split(","):
+        callback_path = callback_path.strip()
+        if not callback_path:
+            continue
+
+        try:
+            module_path, class_name = callback_path.rsplit(".", 1)
+            module = importlib.import_module(module_path)
+            callback_cls = getattr(module, class_name)
+            if not issubclass(callback_cls, RayTrainCallback):
+                raise TypeError(
+                    f"Callback class '{callback_path}' must be a subclass of "
+                    f"RayTrainCallback, got {type(callback_cls).__name__}"
+                )
+            callback = callback_cls()
+            callbacks.append(callback)
+        except (ImportError, AttributeError, ValueError, TypeError) as e:
+            raise ValueError(f"Failed to import callback from '{callback_path}'") from e
+
+    return callbacks