Use fastjsonschema if installed and tests.

.travis.yml

@@ -10,11 +10,14 @@ sudo: false
 install:
     - pip install --upgrade setuptools pip
     - pip install --upgrade pytest
+    - pip install --upgrade fastjsonschema
     - pip install . codecov
     - pip install nbformat[test]
     - pip freeze
 script:
     - py.test -v --cov nbformat nbformat
+    - pip uninstall fastjsonschema --yes
+    - py.test -v --cov nbformat nbformat
 after_success:
     - codecov
 matrix:

appveyor.yml

@@ -15,13 +15,16 @@ install:
   - 'SET "PATH=%PYTHON%\\Scripts;%PATH%"'
   # Install our package:
   - pip install codecov
+  - pip install fastjsonschema
   - 'pip install --upgrade ".[test]"'
 
 build: off
 
 # to run your custom scripts instead of automatic tests
 test_script:
   - 'py.test -v --cov nbformat nbformat'
+  - 'pip uninstall fastjsonschema --yes'
+  - 'py.test -v --cov nbformat nbformat'
 
 on_success:
   - codecov

nbformat/__init__.py

@@ -74,7 +74,7 @@ def reads(s, as_version, **kwargs):
     if as_version is not NO_CONVERT:
         nb = convert(nb, as_version)
     try:
-        validate(nb)
+        validate(nb, use_fast=True)
     except ValidationError as e:
         get_logger().error("Notebook JSON is invalid: %s", e)
     return nb
@@ -104,7 +104,7 @@ def writes(nb, version=NO_CONVERT, **kwargs):
     else:
         version, _ = reader.get_version(nb)
     try:
-        validate(nb)
+        validate(nb, use_fast=True)
     except ValidationError as e:
         get_logger().error("Notebook JSON is invalid: %s", e)
     return versions[version].writes_json(nb, **kwargs)

nbformat/tests/many_tracebacks.ipynb

@@ -0,0 +1,46 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {},
+   "outputs": [
+    {
+     "ename": "NameError",
+     "evalue": "name 'iAmNotDefined' is not defined",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mNameError\u001b[0m                                 Traceback (most recent call last)",
+      "\u001b[0;32m<ipython-input-22-56e1109ae320>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0miAmNotDefined\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[0;31mNameError\u001b[0m: name 'iAmNotDefined' is not defined"
+     ]
+    }
+   ],
+   "source": [
+    "# Imagine this cell called a function which runs things on a cluster and you have an error"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.8.5"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}

nbformat/tests/test_validator.py

@@ -4,12 +4,18 @@
 # Distributed under the terms of the Modified BSD License.
 
 import os
+import time
 
 from .base import TestsBase
 from jsonschema import ValidationError
 from nbformat import read
 from ..validator import isvalid, validate, iter_validate
 
+try:
+    import fastjsonschema
+except ImportError:
+    fastjsonschema = None
+
 
 class TestValidator(TestsBase):
 
@@ -118,3 +124,27 @@ def test_validation_no_version(self):
         """Test that an invalid notebook with no version fails validation"""
         with self.assertRaises(ValidationError) as e:
             validate({'invalid': 'notebook'})
+
+    def test_fast_validation(self):
+        """
+        Test that valid notebook with too many outputs is parsed ~12 times
+        faster with fastjsonschema.
+        """
+        if fastjsonschema:
+            with self.fopen(u'many_tracebacks.ipynb', u'r') as f:
+                nb = read(f, as_version=4)
+
+            # Multiply output
+            base_output = nb["cells"][0]["outputs"][0]
+            for i in range(50000):
+                nb["cells"][0]["outputs"].append(base_output)
+
+            start_time = time.time()
+            validate(nb, use_fast=True)
+            fast_time = time.time() - start_time
+
+            start_time = time.time()
+            validate(nb)
+            slow_time = time.time() - start_time
+
+            self.assertGreater(slow_time / fast_time, 12)

nbformat/validator.py

@@ -21,11 +21,20 @@
     """
     raise ImportError(verbose_msg) from e
 
+# Use fastjsonschema if installed
+try:
+    import fastjsonschema
+    from fastjsonschema import JsonSchemaException
+except ImportError:
+    fastjsonschema = None
+    JsonSchemaException = ValidationError
+
 from ipython_genutils.importstring import import_item
 from .reader import get_version, reads
 
 
 validators = {}
+fast_validators = {}
 
 def _relax_additional_properties(obj):
     """relax any `additionalProperties`"""
@@ -50,7 +59,7 @@ def _allow_undefined(schema):
     )
     return schema
 
-def get_validator(version=None, version_minor=None, relax_add_props=False):
+def get_validator(version=None, version_minor=None, relax_add_props=False, use_fast=False):
     """Load the JSON schema into a Validator"""
     if version is None:
         from . import current_nbformat
@@ -66,7 +75,7 @@ def get_validator(version=None, version_minor=None, relax_add_props=False):
     if version_tuple not in validators:
         try:
             schema_json = _get_schema_json(v, version=version, version_minor=version_minor)
-        except AttributeError:
+        except AttributeError as e:
             return None
 
         if current_minor < version_minor:
@@ -77,6 +86,10 @@ def get_validator(version=None, version_minor=None, relax_add_props=False):
 
         validators[version_tuple] = Validator(schema_json)
 
+        # If fastjsonschema is installed use it to validate
+        if use_fast and fastjsonschema is not None and version_tuple not in fast_validators:
+            fast_validators[version_tuple] = fastjsonschema.compile(schema_json)
+
     if relax_add_props:
         try:
             schema_json = _get_schema_json(v, version=version, version_minor=version_minor)
@@ -88,7 +101,15 @@ def get_validator(version=None, version_minor=None, relax_add_props=False):
         schema_json = _relax_additional_properties(schema_json)
 
         validators[version_tuple] = Validator(schema_json)
-    return validators[version_tuple]
+
+        # If fastjsonschema is installed use it to validate
+        if use_fast and fastjsonschema is not None:
+            fast_validators[version_tuple] = fastjsonschema.compile(schema_json)
+
+    if use_fast and fastjsonschema is not None:
+        return fast_validators[version_tuple]
+    else:
+        return validators[version_tuple]
 
 
 def _get_schema_json(v, version=None, version_minor=None):
@@ -241,7 +262,7 @@ def better_validation_error(error, version, version_minor):
 
 
 def validate(nbdict=None, ref=None, version=None, version_minor=None,
-             relax_add_props=False, nbjson=None):
+             relax_add_props=False, nbjson=None, use_fast=False):
     """Checks whether the given notebook dict-like object
     conforms to the relevant notebook format schema.
 
@@ -270,10 +291,22 @@ def validate(nbdict=None, ref=None, version=None, version_minor=None,
         if version is None:
             version, version_minor = 1, 0
 
-    for error in iter_validate(nbdict, ref=ref, version=version,
-                               version_minor=version_minor,
-                               relax_add_props=relax_add_props):
-        raise error
+    validator = get_validator(version, version_minor, relax_add_props=relax_add_props,
+                              use_fast=True)
+
+    if fastjsonschema is not None and use_fast:
+        if validator is None:
+            raise ValidationError("No schema for validating v%s notebooks" % version)
+
+        try:
+            validator(nbdict)
+        except JsonSchemaException as e:
+            raise ValidationError(e.message, schema_path=e.path)
+    else:
+        for error in iter_validate(nbdict, ref=ref, version=version,
+                                   version_minor=version_minor,
+                                   relax_add_props=relax_add_props):
+            raise error
 
 
 def iter_validate(nbdict=None, ref=None, version=None, version_minor=None,
@@ -294,7 +327,8 @@ def iter_validate(nbdict=None, ref=None, version=None, version_minor=None,
     if version is None:
         version, version_minor = get_version(nbdict)
 
-    validator = get_validator(version, version_minor, relax_add_props=relax_add_props)
+    validator = get_validator(version, version_minor, relax_add_props=relax_add_props,
+                              use_fast=False)
 
     if validator is None:
         # no validator