[BUG] skip _try_credentials check for to_gbq (#207)

* [BUG] skip _try_credentials check for to_gbq

Don't do a query read when all you need to write is write credentials.

* Fix auth tests.

* Fix mock for Python 2.7.

Author: tswast

docs/source/changelog.rst

@@ -12,6 +12,7 @@ Changelog
   (:issue:`128`)
 - Reduced verbosity of logging from ``read_gbq``, particularly for short
   queries. (:issue:`201`)
+- Avoid ``SELECT 1`` query when running ``to_gbq``. (:issue:`202`)
 
 .. _changelog-0.6.0:
 

pandas_gbq/auth.py

@@ -16,20 +16,28 @@
 
 
 def get_credentials(
-    private_key=None, project_id=None, reauth=False, auth_local_webserver=False
+    private_key=None,
+    project_id=None,
+    reauth=False,
+    auth_local_webserver=False,
+    try_credentials=None,
 ):
+    if try_credentials is None:
+        try_credentials = _try_credentials
+
     if private_key:
         return get_service_account_credentials(private_key)
 
     # Try to retrieve Application Default Credentials
     credentials, default_project = get_application_default_credentials(
-        project_id=project_id
+        try_credentials, project_id=project_id
     )
 
     if credentials:
         return credentials, default_project
 
     credentials = get_user_account_credentials(
+        try_credentials,
         project_id=project_id,
         reauth=reauth,
         auth_local_webserver=auth_local_webserver,
@@ -79,7 +87,7 @@ def get_service_account_credentials(private_key):
         )
 
 
-def get_application_default_credentials(project_id=None):
+def get_application_default_credentials(try_credentials, project_id=None):
     """
     This method tries to retrieve the "default application credentials".
     This could be useful for running code on Google Cloud Platform.
@@ -111,10 +119,11 @@ def get_application_default_credentials(project_id=None):
     # used with BigQuery. For example, we could be running on a GCE instance
     # that does not allow the BigQuery scopes.
     billing_project = project_id or default_project
-    return _try_credentials(billing_project, credentials), billing_project
+    return try_credentials(billing_project, credentials), billing_project
 
 
 def get_user_account_credentials(
+    try_credentials,
     project_id=None,
     reauth=False,
     auth_local_webserver=False,
@@ -151,7 +160,9 @@ def get_user_account_credentials(
             os.rename("bigquery_credentials.dat", credentials_path)
 
     credentials = load_user_account_credentials(
-        project_id=project_id, credentials_path=credentials_path
+        try_credentials,
+        project_id=project_id,
+        credentials_path=credentials_path,
     )
 
     client_config = {
@@ -187,7 +198,9 @@ def get_user_account_credentials(
     return credentials
 
 
-def load_user_account_credentials(project_id=None, credentials_path=None):
+def load_user_account_credentials(
+    try_credentials, project_id=None, credentials_path=None
+):
     """
     Loads user account credentials from a local file.
 
@@ -230,7 +243,7 @@ def load_user_account_credentials(project_id=None, credentials_path=None):
     request = google.auth.transport.requests.Request()
     credentials.refresh(request)
 
-    return _try_credentials(project_id, credentials)
+    return try_credentials(project_id, credentials)
 
 
 def get_default_credentials_path():

pandas_gbq/gbq.py

@@ -171,6 +171,7 @@ def __init__(
         auth_local_webserver=False,
         dialect="legacy",
         location=None,
+        try_credentials=None,
     ):
         from google.api_core.exceptions import GoogleAPIError
         from google.api_core.exceptions import ClientError
@@ -189,6 +190,7 @@ def __init__(
             project_id=project_id,
             reauth=reauth,
             auth_local_webserver=auth_local_webserver,
+            try_credentials=try_credentials,
         )
 
         if self.project_id is None:
@@ -804,6 +806,9 @@ def to_gbq(
         private_key=private_key,
         auth_local_webserver=auth_local_webserver,
         location=location,
+        # Avoid reads when writing tables.
+        # https://github.com/pydata/pandas-gbq/issues/202
+        try_credentials=lambda project, creds: creds,
     )
     dataset_id, table_id = destination_table.rsplit(".", 1)
 

tests/system/test_auth.py

@@ -66,9 +66,13 @@ def test_get_application_default_credentials_does_not_throw_error():
         with mock.patch(
             "google.auth.default", side_effect=DefaultCredentialsError()
         ):
-            credentials, _ = auth.get_application_default_credentials()
+            credentials, _ = auth.get_application_default_credentials(
+                try_credentials=auth._try_credentials
+            )
     else:
-        credentials, _ = auth.get_application_default_credentials()
+        credentials, _ = auth.get_application_default_credentials(
+            try_credentials=auth._try_credentials
+        )
     assert credentials is None
 
 
@@ -77,7 +81,9 @@ def test_get_application_default_credentials_returns_credentials():
         pytest.skip("Cannot get default_credentials " "from the environment!")
     from google.auth.credentials import Credentials
 
-    credentials, default_project = auth.get_application_default_credentials()
+    credentials, default_project = auth.get_application_default_credentials(
+        try_credentials=auth._try_credentials
+    )
 
     assert isinstance(credentials, Credentials)
     assert default_project is not None
@@ -88,7 +94,9 @@ def test_get_user_account_credentials_bad_file_returns_credentials():
     from google.auth.credentials import Credentials
 
     with mock.patch("__main__.open", side_effect=IOError()):
-        credentials = auth.get_user_account_credentials()
+        credentials = auth.get_user_account_credentials(
+            try_credentials=auth._try_credentials
+        )
     assert isinstance(credentials, Credentials)
 
 
@@ -97,7 +105,9 @@ def test_get_user_account_credentials_returns_credentials(project_id):
     from google.auth.credentials import Credentials
 
     credentials = auth.get_user_account_credentials(
-        project_id=project_id, auth_local_webserver=True
+        project_id=project_id,
+        auth_local_webserver=True,
+        try_credentials=auth._try_credentials,
     )
     assert isinstance(credentials, Credentials)
 
@@ -107,6 +117,9 @@ def test_get_user_account_credentials_reauth_returns_credentials(project_id):
     from google.auth.credentials import Credentials
 
     credentials = auth.get_user_account_credentials(
-        project_id=project_id, auth_local_webserver=True, reauth=True
+        project_id=project_id,
+        auth_local_webserver=True,
+        reauth=True,
+        try_credentials=auth._try_credentials,
     )
     assert isinstance(credentials, Credentials)

tests/unit/test_auth.py

@@ -95,7 +95,9 @@ def mock_default_credentials(scopes=None, request=None):
         google.auth.credentials.Credentials
     )
 
-    def mock_load_credentials(project_id=None, credentials_path=None):
+    def mock_load_credentials(
+        try_credentials, project_id=None, credentials_path=None
+    ):
         return mock_user_credentials
 
     monkeypatch.setattr(

tests/unit/test_gbq.py

@@ -46,6 +46,7 @@ def mock_bigquery_client(monkeypatch):
     # Mock table creation.
     mock_client.get_table.side_effect = NotFound("nope")
     monkeypatch.setattr(gbq.GbqConnector, "get_client", lambda _: mock_client)
+    return mock_client
 
 
 def mock_none_credentials(*args, **kwargs):
@@ -210,6 +211,19 @@ def test_to_gbq_with_verbose_old_pandas_no_warnings(recwarn, min_bq_version):
         assert len(recwarn) == 0
 
 
+def test_to_gbq_doesnt_run_query(
+    recwarn, mock_bigquery_client, min_bq_version
+):
+    try:
+        gbq.to_gbq(
+            DataFrame([[1]]), "dataset.tablename", project_id="my-project"
+        )
+    except gbq.TableCreationError:
+        pass
+
+    mock_bigquery_client.query.assert_not_called()
+
+
 def test_read_gbq_with_no_project_id_given_should_fail(monkeypatch):
     from pandas_gbq import auth