feat: add blacken nox session (#4378)

* feat: add blacken nox session

fixes #4377

* add blacken session to existing noxfiles

Author: Takashi Matsuo

AUTHORING_GUIDE.md

@@ -22,7 +22,7 @@ This section covers guidelines for Python samples. Note that
 
 ### Folder Location
 
-Samples that primarily show the use of one client library should be placed in the 
+Samples that primarily show the use of one client library should be placed in the
 client library repository. Other samples should be placed in this repository
 `python-docs-samples`.
 
@@ -100,6 +100,20 @@ local variables” warnings.
 The use of [Black](https://pypi.org/project/black/) to standardize code
 formatting and simplify diffs is recommended, but optional.
 
+The default noxfile has `blacken` session for convenience. Here are
+some examples.
+
+If you have pyenv configured:
+```sh
+nox -s blacken
+```
+
+If you only have docker:
+```
+cd proj_directory
+../scripts/run_tests_local.sh . blacken
+```
+
 In addition to the syntax guidelines covered in PEP 8, samples should strive
 to follow the Pythonic philosophy outlined in the
 [PEP 20 - Zen of Python](https://www.python.org/dev/peps/pep-0020/) as well
@@ -485,7 +499,7 @@ Automated testing for samples is managed by
 including the flake8 linter, Python 2.7, Python 3.x, and App Engine tests,
 as well as automated README generation.
 
-__Note:__ 
+__Note:__
 
 **Library repositories:** If you are working on an existing project, a `noxfile.py` will already exist.
 For new samples, create a new `noxfile.py` and paste the contents of

appengine/flexible/memcache/noxfile.py

@@ -84,6 +84,18 @@ def lint(session):
     session.run("flake8", *args)
 
 
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #

dataflow/encryption-keys/noxfile.py

@@ -84,6 +84,18 @@ def lint(session):
     session.run("flake8", *args)
 
 
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #

dataflow/flex-templates/streaming_beam/noxfile.py

@@ -84,6 +84,18 @@ def lint(session):
     session.run("flake8", *args)
 
 
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #

ml_engine/online_prediction/noxfile.py

@@ -84,6 +84,18 @@ def lint(session):
     session.run("flake8", *args)
 
 
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #

noxfile-template.py

@@ -144,6 +144,18 @@ def lint(session):
     session.run("flake8", *args)
 
 
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #

pubsub/streaming-analytics/noxfile.py

@@ -84,6 +84,18 @@ def lint(session):
     session.run("flake8", *args)
 
 
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #

run/markdown-preview/editor/noxfile.py

@@ -144,6 +144,18 @@ def lint(session):
     session.run("flake8", *args)
 
 
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #

run/markdown-preview/renderer/noxfile.py

@@ -144,6 +144,18 @@ def lint(session):
     session.run("flake8", *args)
 
 
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #