feat: expose async client

Expose a property that returns the underlying async Spanner gRPC client.

google/cloud/spanner_v1/database.py

@@ -47,6 +47,7 @@
 from google.cloud.spanner_v1 import TransactionSelector
 from google.cloud.spanner_v1 import TransactionOptions
 from google.cloud.spanner_v1 import RequestOptions
+from google.cloud.spanner_v1 import SpannerAsyncClient
 from google.cloud.spanner_v1 import SpannerClient
 from google.cloud.spanner_v1._helpers import _merge_query_options
 from google.cloud.spanner_v1._helpers import (
@@ -143,6 +144,7 @@ class Database(object):
     """
 
     _spanner_api = None
+    _spanner_async_api: SpannerAsyncClient = None
 
     def __init__(
         self,
@@ -438,6 +440,28 @@ def spanner_api(self):
             )
         return self._spanner_api
 
+    @property
+    def spanner_async_api(self):
+        if self._spanner_async_api is None:
+            client_info = self._instance._client._client_info
+            client_options = self._instance._client._client_options
+            if self._instance.emulator_host is not None:
+                channel = grpc.aio.insecure_channel(target=self._instance.emulator_host)
+                transport = SpannerGrpcTransport(channel=channel)
+                self._spanner_async_api = SpannerAsyncClient(
+                    client_info=client_info, transport=transport
+                )
+                return self._spanner_async_api
+            credentials = self._instance._client.credentials
+            if isinstance(credentials, google.auth.credentials.Scoped):
+                credentials = credentials.with_scopes((SPANNER_DATA_SCOPE,))
+            self._spanner_async_api = SpannerAsyncClient(
+                credentials=credentials,
+                client_info=client_info,
+                client_options=client_options,
+            )
+        return self._spanner_async_api
+
     def __eq__(self, other):
         if not isinstance(other, self.__class__):
             return NotImplemented

google/cloud/spanner_v1/services/spanner/transports/grpc.py

@@ -127,7 +127,7 @@ def __init__(
         if client_cert_source:
             warnings.warn("client_cert_source is deprecated", DeprecationWarning)
 
-        if isinstance(channel, grpc.Channel):
+        if isinstance(channel, grpc.Channel) or isinstance(channel, grpc.aio.Channel):
             # Ignore credentials if a channel was passed.
             credentials = None
             self._ignore_credentials = True

noxfile.py

@@ -32,7 +32,7 @@
 ISORT_VERSION = "isort==5.11.0"
 LINT_PATHS = ["docs", "google", "tests", "noxfile.py", "setup.py"]
 
-DEFAULT_PYTHON_VERSION = "3.8"
+DEFAULT_PYTHON_VERSION = "3.12"
 
 UNIT_TEST_PYTHON_VERSIONS: List[str] = [
     "3.7",