raise ValidationError in v4 validate

also only load the schema once and store it in a module global

IPython/nbformat/v4/validator.py

@@ -1,66 +1,69 b''
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 from __future__ import print_function
 import json
 import os
 
 try:
-    from jsonschema import SchemaError
+    from jsonschema import ValidationError
     from jsonschema import Draft4Validator as Validator
 except ImportError as e:
     verbose_msg = """
 
     IPython notebook format depends on the jsonschema package:
 
         https://pypi.python.org/pypi/jsonschema
 
     Please install it first.
     """
     raise ImportError(str(e) + verbose_msg)
 
 
 from .nbbase import nbformat, nbformat_schema
 schema_path = os.path.join(
     os.path.dirname(__file__), nbformat_schema,
 )
 
+validator = None
+
+def _load_schema():
+    """Load the JSON schema into the global Validator"""
+    global validator
+    if validator is None:
+        # load the schema file
+        with open(schema_path, 'r') as fh:
+            schema_json = json.load(fh)
+
+        # create the validator
+        validator = Validator(schema_json)
+    return validator
 
 def isvalid(nbjson, ref=None):
     """Checks whether the given notebook JSON conforms to the current
     notebook format schema. Returns True if the JSON is valid, and
     False otherwise.
 
     To see the individual errors that were encountered, please use the
     `validate` function instead.
     """
-
-    it = validate(nbjson, ref)
     try:
-        it.next()
-    except StopIteration:
-        return True
-    else:
+        validate(nbjson, ref)
+    except ValidationError:
         return False
+    else:
+        return True
 
 
 def validate(nbjson, ref=None):
     """Checks whether the given notebook JSON conforms to the current
     notebook format schema.
 
-    Returns a generator for errors.
+    Raises ValidationError if not valid.
     """
+    _load_schema()
 
-    # load the schema file
-    with open(schema_path, 'r') as fh:
-        schema_json = json.load(fh)
-
-    # create the validator
-    v = Validator(schema_json)
-
-    # return the iterator on errors
     if ref:
-        errors = v.iter_errors(nbjson, {'$ref' : '#/definitions/%s' % ref})
+        return validator.validate(nbjson, {'$ref' : '#/definitions/%s' % ref})
     else:
-        errors = v.iter_errors(nbjson)
-    return errors
+        return validator.validate(nbjson)