feat: lazy imports gapic v1

packages/google-api-core/google/api_core/gapic_v1/__init__.py

@@ -12,18 +12,51 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from google.api_core.gapic_v1 import client_info
-from google.api_core.gapic_v1 import config
-from google.api_core.gapic_v1 import config_async
-from google.api_core.gapic_v1 import method
-from google.api_core.gapic_v1 import method_async
-from google.api_core.gapic_v1 import routing_header
+import importlib.util
+from typing import Set
 
-__all__ = [
-    "client_info",
-    "config",
-    "config_async",
-    "method",
-    "method_async",
-    "routing_header",
-]
+_has_grpc = importlib.util.find_spec("grpc") is not None
+
+# PEP 0810: Explicit Lazy Imports
+# Python 3.15+ natively intercepts and defers these imports.
+# Developers can disable this behavior and force eager imports.
+# For more information, see:
+# https://docs.python.org/3.15/library/sys.html#sys.set_lazy_imports_filter
+# Older Python versions safely ignore this variable.
+__lazy_modules__: Set[str] = {
+    "google.api_core.gapic_v1.client_info",
+    "google.api_core.gapic_v1.routing_header",
+}
+
+if _has_grpc:
+    __lazy_modules__.update(
+        {
+            "google.api_core.gapic_v1.config",
+            "google.api_core.gapic_v1.config_async",
+            "google.api_core.gapic_v1.method",
+            "google.api_core.gapic_v1.method_async",
+        }
+    )
+
+from google.api_core.gapic_v1 import client_info  # noqa: E402
+from google.api_core.gapic_v1 import routing_header  # noqa: E402
+
+if _has_grpc:
+    from google.api_core.gapic_v1 import config  # noqa: F401
+    from google.api_core.gapic_v1 import config_async  # noqa: F401
+    from google.api_core.gapic_v1 import method  # noqa: F401
+    from google.api_core.gapic_v1 import method_async  # noqa: F401
+
+    __all__ = [
+        "client_info",
+        "routing_header",
+        "config",
+        "config_async",
+        "method",
+        "method_async",
+    ]
+else:
+    __all__ = [
+        "client_info",
+        "routing_header",
+    ]

packages/google-api-core/tests/unit/gapic/test_lazy_imports.py

@@ -0,0 +1,97 @@
+# Copyright 2026 Google LLC
+#
+# 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 subprocess
+import sys
+
+import pytest
+
+SCRIPT_PYTHON_315 = """
+import sys
+import google.api_core.gapic_v1
+
+# The inner gapic_v1 modules should NOT be loaded yet
+HEAVY_MODULES = [
+    "google.api_core.gapic_v1.client_info",
+    "google.api_core.gapic_v1.config",
+    "google.api_core.gapic_v1.config_async",
+    "google.api_core.gapic_v1.method",
+    "google.api_core.gapic_v1.method_async",
+    "google.api_core.gapic_v1.routing_header",
+]
+
+for mod in HEAVY_MODULES:
+    if mod in sys.modules:
+        print(f"FAILED: {mod} was eagerly loaded into sys.modules")
+        sys.exit(1)
+
+# Trigger reification
+import google.api_core.gapic_v1.client_info
+_ = google.api_core.gapic_v1.client_info.__name__
+
+if "google.api_core.gapic_v1.client_info" not in sys.modules:
+    print("FAILED: google.api_core.gapic_v1.client_info was not lazily loaded upon access")
+    sys.exit(2)
+
+sys.exit(0)
+"""
+
+SCRIPT_PRE_315 = """
+import sys
+import google.api_core.gapic_v1
+
+try:
+    import grpc
+    has_grpc = True
+except ImportError:
+    has_grpc = False
+
+HEAVY_MODULES = [
+    "google.api_core.gapic_v1.client_info",
+    "google.api_core.gapic_v1.routing_header",
+]
+
+if has_grpc:
+    HEAVY_MODULES.extend([
+        "google.api_core.gapic_v1.config",
+        "google.api_core.gapic_v1.config_async",
+        "google.api_core.gapic_v1.method",
+        "google.api_core.gapic_v1.method_async",
+    ])
+
+for mod in HEAVY_MODULES:
+    if mod not in sys.modules:
+        print(f"FAILED: {mod} was not eagerly loaded into sys.modules")
+        sys.exit(1)
+
+sys.exit(0)
+"""
+
+
+@pytest.mark.skipif(sys.version_info < (3, 15), reason="PEP 810 requires Python 3.15+")
+def test_lazy_imports_on_python_315():
+    result = subprocess.run(
+        [sys.executable, "-c", SCRIPT_PYTHON_315], capture_output=True, text=True
+    )
+    assert result.returncode == 0, f"Subprocess failed: {result.stdout}"
+
+
+@pytest.mark.skipif(
+    sys.version_info >= (3, 15), reason="Testing fallback behavior on < 3.15"
+)
+def test_fallback_eager_imports_pre_315():
+    result = subprocess.run(
+        [sys.executable, "-c", SCRIPT_PRE_315], capture_output=True, text=True
+    )
+    assert result.returncode == 0, f"Subprocess failed: {result.stdout}"