Add directory structure check (linter)

Author: dbader

.circleci/config.yml

@@ -39,3 +39,9 @@ jobs:
             . venv/bin/activate
             flake8
             black --check .
+
+      - run:
+          name: Directory layout check
+          command: |
+            . venv/bin/activate
+            python .circleci/dircheck.py

.circleci/dircheck.py

@@ -0,0 +1,74 @@
+"""
+Linter to ensure standard folder structure
+"""
+import pathlib
+import re
+import sys
+
+IGNORELIST = {
+    "venv",
+    "asyncio-walkthrough",
+    "build-a-gui-with-wxpython",
+    "consuming-apis-python",
+    "flask-connexion-rest-part-3",
+    "flask-connexion-rest-part-4",
+    "generators",
+    "intro-to-threading",
+    "introduction-combining-data-pandas-merge-join-and-concat",
+    "linked-lists-python",
+    "nearbyshops",
+    "oop-in-java-vs-python",
+    "opencv-color-spaces",
+    "openpyxl-excel-spreadsheets-python",
+    "pygame-a-primer",
+    "pyqt-calculator-tutorial",
+    "python-bindings",
+    "python-dash",
+    "python-eval-mathrepl",
+    "qt-designer-python",
+    "rp-portfolio",
+    "storing-images",
+    "understanding-asynchronous-programming",
+}
+FOLDER_NAME_RE = re.compile(r"^[-a-z0-9]{5,}\Z")
+
+has_errors = False
+
+for f in sorted(pathlib.Path(".").glob("*")):
+    if not f.is_dir():
+        continue
+    if str(f).startswith("."):
+        continue
+    if str(f) in IGNORELIST:
+        continue
+
+    if not FOLDER_NAME_RE.search(str(f)):
+        print(
+            f"{f}: ensure folder name only uses "
+            f"lowercase letters, numbers, and hyphens"
+        )
+        has_error = True
+
+    files = sorted(_.name for _ in f.glob("*"))
+    if "README.md" not in files:
+        print(f"{f}: no README.md found")
+        has_errors = True
+
+if has_errors:
+    print(
+        """-----------------------
+Please ensure new sample projects are added using the correct
+folder structure:
+
+  * New files should go into a top-level subfolder, named after the
+    article slug (lowercase, dashes). For example: my-awesome-article/
+
+  * Top-level sample project folders should contain a README.md file.
+    For example: my-awesome-article/README.md
+
+This helps us keep the repo clean and easy to browse on GitHub.
+
+Thanks!
+"""
+    )
+    sys.exit(1)