We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Remove pinning and pip_pre config once jsonschema 3 is released properly
Refs https://github.com/Kinto/kinto/pull/1898#pullrequestreview-180204186

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `kinto/schema_validation.py`
Content:
```
1 import colander
2 from jsonschema import ValidationError, SchemaError, RefResolutionError
3 from jsonschema.validators import validator_for
4 
5 try:  # pragma: no cover
6     from jsonschema import Draft7Validator as DraftValidator
7 except ImportError:
8     from jsonschema import Draft4Validator as DraftValidator
9 
10 from pyramid.settings import asbool
11 
12 from kinto.core import utils
13 from kinto.core.errors import raise_invalid
14 from kinto.views import object_exists_or_404
15 
16 
17 class JSONSchemaMapping(colander.SchemaNode):
18     def schema_type(self, **kw):
19         return colander.Mapping(unknown="preserve")
20 
21     def deserialize(self, cstruct=colander.null):
22         # Start by deserializing a simple mapping.
23         validated = super().deserialize(cstruct)
24 
25         # In case it is optional in parent schema.
26         if not validated or validated in (colander.null, colander.drop):
27             return validated
28         try:
29             check_schema(validated)
30         except ValidationError as e:
31             self.raise_invalid(e.message)
32         return validated
33 
34 
35 def check_schema(data):
36     try:
37         DraftValidator.check_schema(data)
38     except SchemaError as e:
39         message = e.path.pop() + e.message
40         raise ValidationError(message)
41 
42 
43 # Module level global that stores a version of every possible schema (as a <class 'dict'>)
44 # turned into a jsonschema instance (as <class 'jsonschema.validators.Validator'>).
45 _schema_cache = {}
46 
47 
48 def validate(data, schema):
49     """Raise a ValidationError or a RefResolutionError if the data doesn't validate
50     with the given schema.
51 
52     Note that this function is just a "wrapper" on `jsonschema.validate()` but with
53     some memoization based on the schema for better repeat performance.
54     """
55     # Because the schema is a dict, it can't be used as a hash key so it needs to be
56     # "transformed" to something that is hashable. The quickest solution is to convert
57     # it to a string.
58     # Note that the order of the dict will determine the string it becomes. The solution
59     # to that would a canonical serializer like `json.dumps(..., sort_keys=True)` but it's
60     # overkill since the assumption is that the schema is very unlikely to be exactly
61     # the same but different order.
62     cache_key = str(schema)
63     if cache_key not in _schema_cache:
64         # This is essentially what the `jsonschema.validate()` shortcut function does.
65         cls = validator_for(schema)
66         cls.check_schema(schema)
67         _schema_cache[cache_key] = cls(schema)
68     return _schema_cache[cache_key].validate(data)
69 
70 
71 def validate_schema(data, schema, id_field, ignore_fields=None):
72     if ignore_fields is None:
73         ignore_fields = []
74     # Only ignore the `id` field if the schema does not explicitly mention it.
75     if id_field not in schema.get("properties", {}):
76         ignore_fields += (id_field,)
77 
78     required_fields = [f for f in schema.get("required", []) if f not in ignore_fields]
79     # jsonschema doesn't accept 'required': [] yet.
80     # See https://github.com/Julian/jsonschema/issues/337.
81     # In the meantime, strip out 'required' if no other fields are required.
82     if required_fields:
83         schema = {**schema, "required": required_fields}
84     else:
85         schema = {f: v for f, v in schema.items() if f != "required"}
86 
87     data = {f: v for f, v in data.items() if f not in ignore_fields}
88 
89     try:
90         validate(data, schema)
91     except ValidationError as e:
92         if e.path:
93             field = e.path[-1]
94         elif e.validator_value:
95             field = e.validator_value[-1]
96         else:
97             field = e.schema_path[-1]
98         e.field = field
99         raise e
100     # Raise an error here if a reference in the schema doesn't resolve.
101     # jsonschema doesn't provide schema validation checking upon creation yet,
102     # it must be validated against data.
103     # See https://github.com/Julian/jsonschema/issues/399
104     # For future support https://github.com/Julian/jsonschema/issues/346.
105     except RefResolutionError as e:
106         raise e
107 
108 
109 def validate_from_bucket_schema_or_400(data, resource_name, request, id_field, ignore_fields):
110     """Lookup in the parent objects if a schema was defined for this resource.
111 
112     If the schema validation feature is enabled, if a schema is/are defined, and if the
113     data does not validate it/them, then it raises a 400 exception.
114     """
115     settings = request.registry.settings
116     schema_validation = "experimental_collection_schema_validation"
117     # If disabled from settings, do nothing.
118     if not asbool(settings.get(schema_validation)):
119         return
120 
121     bucket_id = request.matchdict["bucket_id"]
122     bucket_uri = utils.instance_uri(request, "bucket", id=bucket_id)
123     buckets = request.bound_data.setdefault("buckets", {})
124     if bucket_uri not in buckets:
125         # Unknown yet, fetch from storage.
126         bucket = object_exists_or_404(
127             request, resource_name="bucket", parent_id="", object_id=bucket_id
128         )
129         buckets[bucket_uri] = bucket
130 
131     # Let's see if the bucket defines a schema for this resource.
132     metadata_field = f"{resource_name}:schema"
133     bucket = buckets[bucket_uri]
134     if metadata_field not in bucket:
135         return
136 
137     # Validate or fail with 400.
138     schema = bucket[metadata_field]
139     try:
140         validate_schema(data, schema, ignore_fields=ignore_fields, id_field=id_field)
141     except ValidationError as e:
142         raise_invalid(request, name=e.field, description=e.message)
143     except RefResolutionError as e:
144         raise_invalid(request, name="schema", description=str(e))
145
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/kinto/schema_validation.py b/kinto/schema_validation.py
--- a/kinto/schema_validation.py
+++ b/kinto/schema_validation.py
@@ -1,12 +1,12 @@
 import colander
-from jsonschema import ValidationError, SchemaError, RefResolutionError
+from jsonschema import (
+    Draft7Validator as DraftValidator,
+    ValidationError,
+    SchemaError,
+    RefResolutionError,
+)
 from jsonschema.validators import validator_for
 
-try:  # pragma: no cover
-    from jsonschema import Draft7Validator as DraftValidator
-except ImportError:
-    from jsonschema import Draft4Validator as DraftValidator
-
 from pyramid.settings import asbool
 
 from kinto.core import utils

{"golden_diff": "diff --git a/kinto/schema_validation.py b/kinto/schema_validation.py\n--- a/kinto/schema_validation.py\n+++ b/kinto/schema_validation.py\n@@ -1,12 +1,12 @@\n import colander\n-from jsonschema import ValidationError, SchemaError, RefResolutionError\n+from jsonschema import (\n+    Draft7Validator as DraftValidator,\n+    ValidationError,\n+    SchemaError,\n+    RefResolutionError,\n+)\n from jsonschema.validators import validator_for\n \n-try:  # pragma: no cover\n-    from jsonschema import Draft7Validator as DraftValidator\n-except ImportError:\n-    from jsonschema import Draft4Validator as DraftValidator\n-\n from pyramid.settings import asbool\n \n from kinto.core import utils\n", "issue": "Remove pinning and pip_pre config once jsonschema 3 is released properly\nRefs https://github.com/Kinto/kinto/pull/1898#pullrequestreview-180204186\n", "before_files": [{"content": "import colander\nfrom jsonschema import ValidationError, SchemaError, RefResolutionError\nfrom jsonschema.validators import validator_for\n\ntry:  # pragma: no cover\n    from jsonschema import Draft7Validator as DraftValidator\nexcept ImportError:\n    from jsonschema import Draft4Validator as DraftValidator\n\nfrom pyramid.settings import asbool\n\nfrom kinto.core import utils\nfrom kinto.core.errors import raise_invalid\nfrom kinto.views import object_exists_or_404\n\n\nclass JSONSchemaMapping(colander.SchemaNode):\n    def schema_type(self, **kw):\n        return colander.Mapping(unknown=\"preserve\")\n\n    def deserialize(self, cstruct=colander.null):\n        # Start by deserializing a simple mapping.\n        validated = super().deserialize(cstruct)\n\n        # In case it is optional in parent schema.\n        if not validated or validated in (colander.null, colander.drop):\n            return validated\n        try:\n            check_schema(validated)\n        except ValidationError as e:\n            self.raise_invalid(e.message)\n        return validated\n\n\ndef check_schema(data):\n    try:\n        DraftValidator.check_schema(data)\n    except SchemaError as e:\n        message = e.path.pop() + e.message\n        raise ValidationError(message)\n\n\n# Module level global that stores a version of every possible schema (as a <class 'dict'>)\n# turned into a jsonschema instance (as <class 'jsonschema.validators.Validator'>).\n_schema_cache = {}\n\n\ndef validate(data, schema):\n    \"\"\"Raise a ValidationError or a RefResolutionError if the data doesn't validate\n    with the given schema.\n\n    Note that this function is just a \"wrapper\" on `jsonschema.validate()` but with\n    some memoization based on the schema for better repeat performance.\n    \"\"\"\n    # Because the schema is a dict, it can't be used as a hash key so it needs to be\n    # \"transformed\" to something that is hashable. The quickest solution is to convert\n    # it to a string.\n    # Note that the order of the dict will determine the string it becomes. The solution\n    # to that would a canonical serializer like `json.dumps(..., sort_keys=True)` but it's\n    # overkill since the assumption is that the schema is very unlikely to be exactly\n    # the same but different order.\n    cache_key = str(schema)\n    if cache_key not in _schema_cache:\n        # This is essentially what the `jsonschema.validate()` shortcut function does.\n        cls = validator_for(schema)\n        cls.check_schema(schema)\n        _schema_cache[cache_key] = cls(schema)\n    return _schema_cache[cache_key].validate(data)\n\n\ndef validate_schema(data, schema, id_field, ignore_fields=None):\n    if ignore_fields is None:\n        ignore_fields = []\n    # Only ignore the `id` field if the schema does not explicitly mention it.\n    if id_field not in schema.get(\"properties\", {}):\n        ignore_fields += (id_field,)\n\n    required_fields = [f for f in schema.get(\"required\", []) if f not in ignore_fields]\n    # jsonschema doesn't accept 'required': [] yet.\n    # See https://github.com/Julian/jsonschema/issues/337.\n    # In the meantime, strip out 'required' if no other fields are required.\n    if required_fields:\n        schema = {**schema, \"required\": required_fields}\n    else:\n        schema = {f: v for f, v in schema.items() if f != \"required\"}\n\n    data = {f: v for f, v in data.items() if f not in ignore_fields}\n\n    try:\n        validate(data, schema)\n    except ValidationError as e:\n        if e.path:\n            field = e.path[-1]\n        elif e.validator_value:\n            field = e.validator_value[-1]\n        else:\n            field = e.schema_path[-1]\n        e.field = field\n        raise e\n    # Raise an error here if a reference in the schema doesn't resolve.\n    # jsonschema doesn't provide schema validation checking upon creation yet,\n    # it must be validated against data.\n    # See https://github.com/Julian/jsonschema/issues/399\n    # For future support https://github.com/Julian/jsonschema/issues/346.\n    except RefResolutionError as e:\n        raise e\n\n\ndef validate_from_bucket_schema_or_400(data, resource_name, request, id_field, ignore_fields):\n    \"\"\"Lookup in the parent objects if a schema was defined for this resource.\n\n    If the schema validation feature is enabled, if a schema is/are defined, and if the\n    data does not validate it/them, then it raises a 400 exception.\n    \"\"\"\n    settings = request.registry.settings\n    schema_validation = \"experimental_collection_schema_validation\"\n    # If disabled from settings, do nothing.\n    if not asbool(settings.get(schema_validation)):\n        return\n\n    bucket_id = request.matchdict[\"bucket_id\"]\n    bucket_uri = utils.instance_uri(request, \"bucket\", id=bucket_id)\n    buckets = request.bound_data.setdefault(\"buckets\", {})\n    if bucket_uri not in buckets:\n        # Unknown yet, fetch from storage.\n        bucket = object_exists_or_404(\n            request, resource_name=\"bucket\", parent_id=\"\", object_id=bucket_id\n        )\n        buckets[bucket_uri] = bucket\n\n    # Let's see if the bucket defines a schema for this resource.\n    metadata_field = f\"{resource_name}:schema\"\n    bucket = buckets[bucket_uri]\n    if metadata_field not in bucket:\n        return\n\n    # Validate or fail with 400.\n    schema = bucket[metadata_field]\n    try:\n        validate_schema(data, schema, ignore_fields=ignore_fields, id_field=id_field)\n    except ValidationError as e:\n        raise_invalid(request, name=e.field, description=e.message)\n    except RefResolutionError as e:\n        raise_invalid(request, name=\"schema\", description=str(e))\n", "path": "kinto/schema_validation.py"}], "after_files": [{"content": "import colander\nfrom jsonschema import (\n    Draft7Validator as DraftValidator,\n    ValidationError,\n    SchemaError,\n    RefResolutionError,\n)\nfrom jsonschema.validators import validator_for\n\nfrom pyramid.settings import asbool\n\nfrom kinto.core import utils\nfrom kinto.core.errors import raise_invalid\nfrom kinto.views import object_exists_or_404\n\n\nclass JSONSchemaMapping(colander.SchemaNode):\n    def schema_type(self, **kw):\n        return colander.Mapping(unknown=\"preserve\")\n\n    def deserialize(self, cstruct=colander.null):\n        # Start by deserializing a simple mapping.\n        validated = super().deserialize(cstruct)\n\n        # In case it is optional in parent schema.\n        if not validated or validated in (colander.null, colander.drop):\n            return validated\n        try:\n            check_schema(validated)\n        except ValidationError as e:\n            self.raise_invalid(e.message)\n        return validated\n\n\ndef check_schema(data):\n    try:\n        DraftValidator.check_schema(data)\n    except SchemaError as e:\n        message = e.path.pop() + e.message\n        raise ValidationError(message)\n\n\n# Module level global that stores a version of every possible schema (as a <class 'dict'>)\n# turned into a jsonschema instance (as <class 'jsonschema.validators.Validator'>).\n_schema_cache = {}\n\n\ndef validate(data, schema):\n    \"\"\"Raise a ValidationError or a RefResolutionError if the data doesn't validate\n    with the given schema.\n\n    Note that this function is just a \"wrapper\" on `jsonschema.validate()` but with\n    some memoization based on the schema for better repeat performance.\n    \"\"\"\n    # Because the schema is a dict, it can't be used as a hash key so it needs to be\n    # \"transformed\" to something that is hashable. The quickest solution is to convert\n    # it to a string.\n    # Note that the order of the dict will determine the string it becomes. The solution\n    # to that would a canonical serializer like `json.dumps(..., sort_keys=True)` but it's\n    # overkill since the assumption is that the schema is very unlikely to be exactly\n    # the same but different order.\n    cache_key = str(schema)\n    if cache_key not in _schema_cache:\n        # This is essentially what the `jsonschema.validate()` shortcut function does.\n        cls = validator_for(schema)\n        cls.check_schema(schema)\n        _schema_cache[cache_key] = cls(schema)\n    return _schema_cache[cache_key].validate(data)\n\n\ndef validate_schema(data, schema, id_field, ignore_fields=None):\n    if ignore_fields is None:\n        ignore_fields = []\n    # Only ignore the `id` field if the schema does not explicitly mention it.\n    if id_field not in schema.get(\"properties\", {}):\n        ignore_fields += (id_field,)\n\n    required_fields = [f for f in schema.get(\"required\", []) if f not in ignore_fields]\n    # jsonschema doesn't accept 'required': [] yet.\n    # See https://github.com/Julian/jsonschema/issues/337.\n    # In the meantime, strip out 'required' if no other fields are required.\n    if required_fields:\n        schema = {**schema, \"required\": required_fields}\n    else:\n        schema = {f: v for f, v in schema.items() if f != \"required\"}\n\n    data = {f: v for f, v in data.items() if f not in ignore_fields}\n\n    try:\n        validate(data, schema)\n    except ValidationError as e:\n        if e.path:\n            field = e.path[-1]\n        elif e.validator_value:\n            field = e.validator_value[-1]\n        else:\n            field = e.schema_path[-1]\n        e.field = field\n        raise e\n    # Raise an error here if a reference in the schema doesn't resolve.\n    # jsonschema doesn't provide schema validation checking upon creation yet,\n    # it must be validated against data.\n    # See https://github.com/Julian/jsonschema/issues/399\n    # For future support https://github.com/Julian/jsonschema/issues/346.\n    except RefResolutionError as e:\n        raise e\n\n\ndef validate_from_bucket_schema_or_400(data, resource_name, request, id_field, ignore_fields):\n    \"\"\"Lookup in the parent objects if a schema was defined for this resource.\n\n    If the schema validation feature is enabled, if a schema is/are defined, and if the\n    data does not validate it/them, then it raises a 400 exception.\n    \"\"\"\n    settings = request.registry.settings\n    schema_validation = \"experimental_collection_schema_validation\"\n    # If disabled from settings, do nothing.\n    if not asbool(settings.get(schema_validation)):\n        return\n\n    bucket_id = request.matchdict[\"bucket_id\"]\n    bucket_uri = utils.instance_uri(request, \"bucket\", id=bucket_id)\n    buckets = request.bound_data.setdefault(\"buckets\", {})\n    if bucket_uri not in buckets:\n        # Unknown yet, fetch from storage.\n        bucket = object_exists_or_404(\n            request, resource_name=\"bucket\", parent_id=\"\", object_id=bucket_id\n        )\n        buckets[bucket_uri] = bucket\n\n    # Let's see if the bucket defines a schema for this resource.\n    metadata_field = f\"{resource_name}:schema\"\n    bucket = buckets[bucket_uri]\n    if metadata_field not in bucket:\n        return\n\n    # Validate or fail with 400.\n    schema = bucket[metadata_field]\n    try:\n        validate_schema(data, schema, ignore_fields=ignore_fields, id_field=id_field)\n    except ValidationError as e:\n        raise_invalid(request, name=e.field, description=e.message)\n    except RefResolutionError as e:\n        raise_invalid(request, name=\"schema\", description=str(e))\n", "path": "kinto/schema_validation.py"}]}