chore(python): add nox session to sort python imports (#269)

Source-Link: googleapis/synthtool@1b71c10
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:00c9d764fd1cd56265f12a5ef4b99a0c9e87cf261018099141e2ca5158890416

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

cloudbuild/snippets/noxfile.py

@@ -30,6 +30,7 @@
 # WARNING - WARNING - WARNING - WARNING - WARNING
 
 BLACK_VERSION = "black==22.3.0"
+ISORT_VERSION = "isort==5.10.1"
 
 # Copy `noxfile_config.py` to your directory and modify it instead.
 
@@ -168,12 +169,32 @@ def lint(session: nox.sessions.Session) -> None:
 
 @nox.session
 def blacken(session: nox.sessions.Session) -> None:
+    """Run black. Format code to uniform standard."""
     session.install(BLACK_VERSION)
     python_files = [path for path in os.listdir(".") if path.endswith(".py")]
 
     session.run("black", *python_files)
 
 
+#
+# format = isort + black
+#
+
+@nox.session
+def format(session: nox.sessions.Session) -> None:
+    """
+    Run isort to sort imports. Then run black
+    to format code to uniform standard.
+    """
+    session.install(BLACK_VERSION, ISORT_VERSION)
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    # Use the --fss option to sort imports using strict alphabetical order.
+    # See https://pycqa.github.io/isort/docs/configuration/options.html#force-sort-within-sections
+    session.run("isort", "--fss", *python_files)
+    session.run("black", *python_files)
+
+
 #
 # Sample Tests
 #