feat: add sample code for ListAssets v1p5beta1 (#4251)

## Description

Fixes #4250

Note: It's a good idea to open an issue first for discussion.

## Checklist
- [x] I have followed [Sample Guidelines from AUTHORING_GUIDE.MD](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md)
- [ ] README is updated to include [all relevant information](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#readme-file)
- [x] **Tests** pass:   `nox -s py-3.6` (see [Test Enviroment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [x] **Lint** pass:   `nox -s lint` (see [Test Enviroment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/AUTHORING_GUIDE.md#test-environment-setup))
- [ ] These samples need a new **API enabled** in testing projects to pass (let us know which ones)
- [ ] These samples need a new/updated **env vars** in testing projects set to pass (let us know which ones)
- [x] Please **merge** this PR for me once it is approved.

Author: Larittic-GG

asset/cloud-client/quickstart_listassets.py

@@ -0,0 +1,66 @@
+#!/usr/bin/env python
+
+# Copyright 2020 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 argparse
+
+
+def list_assets(project_id, asset_types, page_size):
+    # [START asset_quickstart_list_assets]
+    from google.cloud import asset_v1p5beta1
+    from google.cloud.asset_v1p5beta1 import enums
+
+    # TODO project_id = 'Your Google Cloud Project ID'
+    # TODO asset_types = 'Your asset type list, e.g.,
+    # ["storage.googleapis.com/Bucket","bigquery.googleapis.com/Table"]'
+    # TODO page_size = 'Num of assets in one page, which must be between 1 and
+    # 1000 (both inclusively)'
+
+    project_resource = 'projects/{}'.format(project_id)
+    content_type = enums.ContentType.RESOURCE
+    client = asset_v1p5beta1.AssetServiceClient()
+
+    # Call ListAssets v1p5beta1 to list assets.
+    response = client.list_assets(
+        parent=project_resource, read_time=None, asset_types=asset_types,
+        content_type=content_type, page_size=page_size)
+
+    for page in response.pages:
+        for asset in page:
+            print(asset)
+    # [END asset_quickstart_list_assets]
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(
+        description=__doc__,
+        formatter_class=argparse.RawDescriptionHelpFormatter
+    )
+    parser.add_argument('project_id', help='Your Google Cloud project ID')
+    parser.add_argument(
+        'asset_types',
+        help='The types of the assets to list, comma delimited, e.g., '
+        'storage.googleapis.com/Bucket')
+    parser.add_argument(
+        'page_size',
+        help='Num of assets in one page, which must be between 1 and 1000 '
+        '(both inclusively)')
+
+    args = parser.parse_args()
+
+    asset_type_list = args.asset_types.split(',')
+
+    list_assets(args.project_id, asset_type_list, int(args.page_size))

asset/cloud-client/quickstart_listassets_test.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python
+
+# Copyright 2020 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 os
+
+import quickstart_listassets
+
+PROJECT = os.environ['GOOGLE_CLOUD_PROJECT']
+
+
+def test_list_assets(capsys):
+    quickstart_listassets.list_assets(project_id=PROJECT, asset_types=[], page_size=10)
+    out, _ = capsys.readouterr()
+    assert 'asset' in out