DEV: Add Notebook AST Pre-Commit Hook (#417)

- Adds a simple pre-commit check which iterates over code cells in each notebook file and checks that any lines which don't start with a ! are valid python, i.e. that they parse to an abstract syntax tree (AST).
- Also removes a broken and unused old hook.

.pre-commit-config.yaml

@@ -67,14 +67,6 @@ repos:
           flake8-use-fstring, # Encourages use of f-strings vs old style
           pep8-naming, # Check PEP8 class naming
         ]
-  - repo: local
-    hooks:
-      - id: pytest-changed-files
-        name: pytest-changed-files
-        entry: pytest
-        files: tests/.*\btest_\w*.py
-        language: system
-        stages: [push]
   - repo: local
     hooks:
       - id: requirements-consistency
@@ -84,3 +76,8 @@ repos:
         pass_filenames: false
         language: python
         additional_dependencies: [pyyaml]
+      - id: notebook-check-ast
+        name: check notebook ast
+        entry: python pre-commit/notebook_check_ast.py
+        types_or: [jupyter]
+        language: python

pre-commit/notebook_check_ast.py

@@ -0,0 +1,33 @@
+"""Simple check to ensure each code cell in a notebook is valid Python."""
+import argparse
+import ast
+import json
+import sys
+from pathlib import Path
+from typing import List
+
+
+def main(files: List[Path]) -> bool:
+    """Check each file in the list of files for valid Python."""
+    passed = True
+    for path in files:
+        with open(path) as fh:
+            notebook = json.load(fh)
+        for n, cell in enumerate(notebook["cells"]):
+            if cell["cell_type"] != "code":
+                continue
+            source = "".join([x for x in cell["source"] if not x.startswith("!")])
+            try:
+                ast.parse(source)
+            except SyntaxError as e:
+                passed = False
+                print(f"{path.name}: {e.msg} (cell {n}, line {e.lineno})")
+                break
+    return passed  # noqa: R504
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description="Check notebook AST")
+    parser.add_argument("files", nargs="+", help="Path to notebook(s)", type=Path)
+    args = parser.parse_args()
+    sys.exit(1 - main(args.files))