Add nbformat-based validation script for Jupyter notebooks

Author: Aniketsy

scripts/validate_notebooks.py

@@ -1,7 +1,25 @@
+# Copyright 2020 The TensorFlow Quantum Authors. All Rights Reserved.
+#
+# 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.
+# ==============================================================================
+"""Validate all Jupyter notebooks in the repository using nbformat."""
 import sys
-import nbformat
 from pathlib import Path
 
+import nbformat
+from nbformat.validator import NotebookValidationError
+
+
 def main():
     """Check all notebooks for valid nbformat structure."""
     failed = False
@@ -13,7 +31,7 @@ def main():
                 nb = nbformat.read(f, as_version=4)
             nbformat.validate(nb)
             print(f"✓ {notebook_path}")
-        except Exception as e:
+        except (NotebookValidationError, OSError) as e:
             print(f"✗ {notebook_path} failed validation: {e}")
             failed = True