Import bqstorage dependency at top of module.

tswast · tswast · commit fa7bb054b6dd · 2019-04-17T15:01:08.000-07:00
diff --git a/bigquery/google/cloud/bigquery/table.py b/bigquery/google/cloud/bigquery/table.py
@@ -17,6 +17,7 @@
 from __future__ import absolute_import
 
 import collections
+import concurrent.futures
 import copy
 import datetime
 import json
@@ -25,6 +26,11 @@
 
 import six
 
+try:
+    from google.cloud import bigquery_storage_v1beta1
+except ImportError:  # pragma: NO COVER
+    bigquery_storage_v1beta1 = None
+
 try:
     import pandas
 except ImportError:  # pragma: NO COVER
@@ -46,6 +52,10 @@
 from google.cloud.bigquery.external_config import ExternalConfig
 
 
+_NO_PANDAS_ERROR = (
+    "The google-cloud-bigquery-storage library is not installed, "
+    "please install google-cloud-bigquery-storage to use bqstorage features."
+)
 _NO_PANDAS_ERROR = (
     "The pandas library is not installed, please install "
     "pandas to use the to_dataframe() function."
@@ -287,7 +297,8 @@ def to_bqstorage(self):
             google.cloud.bigquery_storage_v1beta1.types.TableReference:
                 A reference to this table in the BigQuery Storage API.
         """
-        from google.cloud import bigquery_storage_v1beta1
+        if bigquery_storage_v1beta1 is None:
+            raise ValueError(_NO_BQSTORAGE_ERROR)
 
         table_ref = bigquery_storage_v1beta1.types.TableReference()
         table_ref.project_id = self._project
@@ -1391,8 +1402,8 @@ def _to_dataframe_bqstorage_stream(
 
     def _to_dataframe_bqstorage(self, bqstorage_client, dtypes):
         """Use (faster, but billable) BQ Storage API to construct DataFrame."""
-        import concurrent.futures
-        from google.cloud import bigquery_storage_v1beta1
+        if bigquery_storage_v1beta1 is None:
+            raise ValueError(_NO_BQSTORAGE_ERROR)
 
         if "$" in self._table.table_id:
             raise ValueError(
