From f5b171979be58732fb28dce0295168ef9ab30494 Mon Sep 17 00:00:00 2001
From: Matthew Tretter <m@tthewwithanm.com>
Date: Thu, 25 Apr 2013 02:29:27 -0400
Subject: [PATCH] Canonicalize sets and dicts before hashing

---
 imagekit/hashers.py        | 31 +++++++++++++++++++++++++++++++
 imagekit/specs/__init__.py |  7 +++----
 2 files changed, 34 insertions(+), 4 deletions(-)
 create mode 100644 imagekit/hashers.py

diff --git a/imagekit/hashers.py b/imagekit/hashers.py
new file mode 100644
index 0000000..4231fa5
--- /dev/null
+++ b/imagekit/hashers.py
@@ -0,0 +1,31 @@
+from copy import copy
+from hashlib import md5
+from pickle import Pickler, MARK, DICT
+from types import DictionaryType
+from .lib import StringIO
+
+
+class CanonicalizingPickler(Pickler):
+    dispatch = copy(Pickler.dispatch)
+
+    def save_set(self, obj):
+        rv = obj.__reduce_ex__(0)
+        rv = (rv[0], (sorted(rv[1][0]),), rv[2])
+        self.save_reduce(obj=obj, *rv)
+
+    dispatch[set] = save_set
+
+    def save_dict(self, obj):
+        write = self.write
+        write(MARK + DICT)
+
+        self.memoize(obj)
+        self._batch_setitems(sorted(obj.iteritems()))
+
+    dispatch[DictionaryType] = save_dict
+
+
+def pickle(obj):
+    file = StringIO()
+    CanonicalizingPickler(file, 0).dump(obj)
+    return md5(file.getvalue()).hexdigest()
diff --git a/imagekit/specs/__init__.py b/imagekit/specs/__init__.py
index dbe56ed..2f6dc51 100644
--- a/imagekit/specs/__init__.py
+++ b/imagekit/specs/__init__.py
@@ -1,9 +1,8 @@
 from django.conf import settings
 from django.db.models.fields.files import ImageFieldFile
-from hashlib import md5
-import pickle
 from ..cachefiles.backends import get_default_cachefile_backend
 from ..cachefiles.strategies import StrategyWrapper
+from .. import hashers
 from ..exceptions import AlreadyRegistered, MissingSource
 from ..processors import ProcessorPipeline
 from ..utils import open_image, img_to_fobj, get_by_qname
@@ -115,13 +114,13 @@ class ImageSpec(BaseImageSpec):
             self.source = getattr(field_data['instance'], field_data['attname'])
 
     def get_hash(self):
-        return md5(pickle.dumps([
+        return hashers.pickle([
             self.source.name,
             self.processors,
             self.format,
             self.options,
             self.autoconvert,
-        ])).hexdigest()
+        ])
 
     def generate(self):
         if not self.source: