Adds import utilities for flash attention integration

Introduces package availability checking with version detection and fallback mechanisms for special cases like torch dev versions.

Includes dedicated function to verify flash attention availability by checking torch, CUDA, and package dependencies.

Author: LoserCheems

flash_dmattn/integrations/import_utils.py

@@ -0,0 +1,95 @@
+# Copyright 2025 Jingze Shi and the HuggingFace Team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+Import utilities: Utilities related to imports and our lazy inits.
+"""
+
+import importlib.metadata
+import importlib.util
+from functools import lru_cache
+from typing import Union
+
+
+from transformers import is_torch_available
+from transformers.utils import logging
+
+
+logger = logging.get_logger(__name__)  # pylint: disable=invalid-name
+
+
+# TODO: This doesn't work for all packages (`bs4`, `faiss`, etc.) Talk to Sylvain to see how to do with it better.
+def _is_package_available(pkg_name: str, return_version: bool = False) -> Union[tuple[bool, str], bool]:
+    # Check if the package spec exists and grab its version to avoid importing a local directory
+    package_exists = importlib.util.find_spec(pkg_name) is not None
+    package_version = "N/A"
+    if package_exists:
+        try:
+            # TODO: Once python 3.9 support is dropped, `importlib.metadata.packages_distributions()`
+            # should be used here to map from package name to distribution names
+            # e.g. PIL -> Pillow, Pillow-SIMD; quark -> amd-quark; onnxruntime -> onnxruntime-gpu.
+            # `importlib.metadata.packages_distributions()` is not available in Python 3.9.
+
+            # Primary method to get the package version
+            package_version = importlib.metadata.version(pkg_name)
+        except importlib.metadata.PackageNotFoundError:
+            # Fallback method: Only for "torch" and versions containing "dev"
+            if pkg_name == "torch":
+                try:
+                    package = importlib.import_module(pkg_name)
+                    temp_version = getattr(package, "__version__", "N/A")
+                    # Check if the version contains "dev"
+                    if "dev" in temp_version:
+                        package_version = temp_version
+                        package_exists = True
+                    else:
+                        package_exists = False
+                except ImportError:
+                    # If the package can't be imported, it's not available
+                    package_exists = False
+            elif pkg_name == "quark":
+                # TODO: remove once `importlib.metadata.packages_distributions()` is supported.
+                try:
+                    package_version = importlib.metadata.version("amd-quark")
+                except Exception:
+                    package_exists = False
+            elif pkg_name == "triton":
+                try:
+                    package_version = importlib.metadata.version("pytorch-triton")
+                except Exception:
+                    package_exists = False
+            else:
+                # For packages other than "torch", don't attempt the fallback and set as not available
+                package_exists = False
+        logger.debug(f"Detected {pkg_name} version: {package_version}")
+    if return_version:
+        return package_exists, package_version
+    else:
+        return package_exists
+
+
+
+@lru_cache
+def is_flash_dmattn_available():
+    if not is_torch_available():
+        return False
+
+    if not _is_package_available("flash_dmattn"):
+        return False
+
+    import torch
+
+    if not torch.cuda.is_available():
+        return False
+
+    return True