Use lru_cache

jsonschema/__init__.py

@@ -19,8 +19,6 @@ from jsonschema.validators import (
     Draft3Validator, Draft4Validator, RefResolver, validate
 )
 
-
-__version__ = "2.5.0-dev"
-
+from jsonschema.version import __version__
 
 # flake8: noqa

jsonschema/_utils.py

@@ -38,22 +38,6 @@ class URIDict(MutableMapping):
         return repr(self.store)
 
 
-class Cache(object):
-    """Cache the result of a function, using the arguments to the function as
-    the key.
-    """
-
-    def __init__(self, func):
-        self.func = func
-        self._cache = {}
-
-    def __call__(self, *args):
-        if args in self._cache:
-            return self._cache[args]
-        self._cache[args] = value = self.func(*args)
-        return value
-
-
 class Unset(object):
     """
     An as-of-yet unset attribute or unprovided default parameter.

jsonschema/compat.py

@@ -13,6 +13,7 @@ PY3 = sys.version_info[0] >= 3
 
 if PY3:
     zip = zip
+    from functools import lru_cache
     from io import StringIO
     from urllib.parse import (
         unquote, urljoin, urlunsplit, SplitResult, urlsplit as _urlsplit
@@ -23,6 +24,7 @@ if PY3:
     iteritems = operator.methodcaller("items")
 else:
     from itertools import izip as zip  # noqa
+    from repoze.lru import lru_cache
     from StringIO import StringIO
     from urlparse import (
         urljoin, urlunsplit, SplitResult, urlsplit as _urlsplit # noqa

jsonschema/tests/test_validators.py

@@ -1,5 +1,4 @@
 from collections import deque
-from contextlib import contextmanager
 import json
 
 from jsonschema import FormatChecker, ValidationError
@@ -870,6 +869,13 @@ class TestRefResolver(unittest.TestCase):
                 pass
         self.assertEqual(str(err.exception), "Oh no! What's this?")
 
+    def test_helpful_error_message_on_failed_pop_scope(self):
+        resolver = RefResolver("", {})
+        resolver.pop_scope()
+        with self.assertRaises(RefResolutionError) as exc:
+            resolver.pop_scope()
+        self.assertIn("Failed to pop the scope", str(exc.exception))
+
 
 def sorted_errors(errors):
     def key(error):

jsonschema/validators.py

@@ -12,7 +12,7 @@ except ImportError:
 from jsonschema import _utils, _validators
 from jsonschema.compat import (
     Sequence, urljoin, urlsplit, urldefrag, unquote, urlopen,
-    str_types, int_types, iteritems,
+    str_types, int_types, iteritems, lru_cache,
 )
 from jsonschema.exceptions import ErrorTree  # Backwards compatibility  # noqa
 from jsonschema.exceptions import RefResolutionError, SchemaError, UnknownType
@@ -233,18 +233,22 @@ class RefResolver(object):
         first resolution
     :argument dict handlers: a mapping from URI schemes to functions that
         should be used to retrieve them
-
+    :arguments callable cache_func: a function decorator used to cache
+        expensive calls. Should support the `functools.lru_cache` interface.
+    :argument int cache_maxsize: number of items to store in the cache. Set
+        this to 0 to disable caching. Defaults to 1000.
     """
 
     def __init__(
         self, base_uri, referrer, store=(), cache_remote=True, handlers=(),
+        cache_func=lru_cache, cache_maxsize=1000,
     ):
         # This attribute is not used, it is for backwards compatibility
         self.referrer = referrer
         self.cache_remote = cache_remote
         self.handlers = dict(handlers)
 
-        self.scopes_stack = [base_uri]
+        self._scopes_stack = [base_uri]
         self.store = _utils.URIDict(
             (id, validator.META_SCHEMA)
             for id, validator in iteritems(meta_schemas)
@@ -252,8 +256,8 @@ class RefResolver(object):
         self.store.update(store)
         self.store[base_uri] = referrer
 
-        self.urljoin_cache = _utils.Cache(urljoin)
-        self.resolve_cache = _utils.Cache(self.resolve_from_url)
+        self._urljoin_cache = cache_func(cache_maxsize)(urljoin)
+        self._resolve_cache = cache_func(cache_maxsize)(self.resolve_from_url)
 
     @classmethod
     def from_schema(cls, schema, *args, **kwargs):
@@ -268,15 +272,21 @@ class RefResolver(object):
         return cls(schema.get(u"id", u""), schema, *args, **kwargs)
 
     def push_scope(self, scope):
-        self.scopes_stack.append(
-            self.urljoin_cache(self.resolution_scope, scope))
+        self._scopes_stack.append(
+            self._urljoin_cache(self.resolution_scope, scope))
 
     def pop_scope(self):
-        self.scopes_stack.pop()
+        try:
+            self._scopes_stack.pop()
+        except IndexError:
+            raise RefResolutionError(
+                "Failed to pop the scope from an empty stack. "
+                "`pop_scope()` should only be called once for every "
+                "`push_scope()`")
 
     @property
     def resolution_scope(self):
-        return self.scopes_stack[-1]
+        return self._scopes_stack[-1]
 
 
     # Deprecated, this function is no longer used, but is preserved for
@@ -308,8 +318,8 @@ class RefResolver(object):
         :argument str ref: reference to resolve
 
         """
-        url = self.urljoin_cache(self.resolution_scope, ref)
-        return url, self.resolve_cache(url)
+        url = self._urljoin_cache(self.resolution_scope, ref)
+        return url, self._resolve_cache(url)
 
     def resolve_from_url(self, url):
         url, fragment = urldefrag(url)

jsonschema/version.py

@@ -0,0 +1 @@
+__version__ = "2.5.0-dev"

setup.py

@@ -1,7 +1,12 @@
+import os.path
 from setuptools import setup
+import sys
 
-from jsonschema import __version__
-
+# Load __version__ info globals without importing anything
+with open(
+    os.path.join(os.path.dirname(__file__), 'jsonschema', 'version.py')
+) as fh:
+    exec(fh.read())
 
 with open("README.rst") as readme:
     long_description = readme.read()
@@ -21,6 +26,11 @@ classifiers = [
     "Programming Language :: Python :: Implementation :: PyPy",
 ]
 
+install_requires = []
+
+if sys.version_info < (3, 2):
+    install_requires.append('repoze.lru >= 0.6')
+
 setup(
     name="jsonschema",
     version=__version__,
@@ -34,4 +44,5 @@ setup(
     long_description=long_description,
     url="http://github.com/Julian/jsonschema",
     entry_points={"console_scripts": ["jsonschema = jsonschema.cli:main"]},
+    install_requires=install_requires,
 )