lazy load trainer classes to prevent unnecesary imports (#3568)

* lazy load trainer classes to prevent unnecesary imports

* make the lazy load a common util

src/axolotl/core/trainers/__init__.py

@@ -2,15 +2,34 @@
 
 # flake8: noqa
 
+from axolotl.utils import make_lazy_getattr
+
 from .base import AxolotlTrainer
-from .dpo.trainer import AxolotlDPOTrainer
-from .ebft.strided import AxolotlStridedEBFTTrainer
-from .ebft.trainer import AxolotlEBFTTrainer
-from .mamba import AxolotlMambaTrainer
-from .trl import (
-    AxolotlCPOTrainer,
-    AxolotlKTOTrainer,
-    AxolotlORPOTrainer,
-    AxolotlPRMTrainer,
-    AxolotlRewardTrainer,
-)
+
+# noinspection PyUnresolvedReferences
+__all__ = [
+    "AxolotlTrainer",
+    "AxolotlCPOTrainer",
+    "AxolotlDPOTrainer",
+    "AxolotlEBFTTrainer",
+    "AxolotlKTOTrainer",
+    "AxolotlMambaTrainer",
+    "AxolotlORPOTrainer",
+    "AxolotlPRMTrainer",
+    "AxolotlRewardTrainer",
+    "AxolotlStridedEBFTTrainer",
+]
+
+_LAZY_IMPORTS = {
+    "AxolotlDPOTrainer": ".dpo.trainer",
+    "AxolotlStridedEBFTTrainer": ".ebft.strided",
+    "AxolotlEBFTTrainer": ".ebft.trainer",
+    "AxolotlMambaTrainer": ".mamba",
+    "AxolotlCPOTrainer": ".trl",
+    "AxolotlKTOTrainer": ".trl",
+    "AxolotlORPOTrainer": ".trl",
+    "AxolotlPRMTrainer": ".trl",
+    "AxolotlRewardTrainer": ".trl",
+}
+
+__getattr__ = make_lazy_getattr(_LAZY_IMPORTS, __name__, globals())

src/axolotl/utils/__init__.py

@@ -9,6 +9,36 @@ import re
 import torch
 
 
+def make_lazy_getattr(
+    lazy_imports: dict[str, str], module_name: str, module_globals: dict
+):
+    """Create a module-level ``__getattr__`` that lazily imports symbols.
+
+    Args:
+        lazy_imports: Mapping of attribute name to relative module path,
+            e.g. ``{"AxolotlDPOTrainer": ".dpo.trainer"}``.
+        module_name: The ``__name__`` of the calling module (used as the
+            anchor for relative imports).
+        module_globals: The ``globals()`` dict of the calling module,
+            used to cache resolved attributes so ``__getattr__`` is only
+            invoked once per name.
+
+    Returns:
+        A ``__getattr__`` function suitable for assignment at module scope.
+    """
+    import importlib
+
+    def __getattr__(name: str):
+        if name in lazy_imports:
+            module = importlib.import_module(lazy_imports[name], module_name)
+            attr = getattr(module, name)
+            module_globals[name] = attr
+            return attr
+        raise AttributeError(f"module {module_name!r} has no attribute {name!r}")
+
+    return __getattr__
+
+
 def is_mlflow_available():
     return importlib.util.find_spec("mlflow") is not None