From 0575011529d26ad092f20b7cac6c9546c4007fdc Mon Sep 17 00:00:00 2001
From: Venelin Stoykov <vkstoykov@gmail.com>
Date: Mon, 19 Aug 2013 21:27:50 +0300
Subject: [PATCH 01/12] Add Python 3 suport and drop support for Python 2.5

---
 imagekit/cachefiles/__init__.py    |  6 +++++-
 imagekit/cachefiles/strategies.py  |  7 +++++--
 imagekit/files.py                  | 10 +++++++---
 imagekit/hashers.py                | 16 ++++++++++------
 imagekit/lib.py                    | 23 ++++++++++++++++++++---
 imagekit/models/fields/__init__.py |  4 +++-
 imagekit/templatetags/imagekit.py  | 12 ++++++++----
 imagekit/utils.py                  |  5 +++--
 setup.py                           |  8 ++++++--
 9 files changed, 67 insertions(+), 24 deletions(-)

diff --git a/imagekit/cachefiles/__init__.py b/imagekit/cachefiles/__init__.py
index 2c602ff..6e2bf19 100644
--- a/imagekit/cachefiles/__init__.py
+++ b/imagekit/cachefiles/__init__.py
@@ -120,7 +120,7 @@ class ImageCacheFile(BaseIKFile, ImageFile):
                 )
             )
 
-    def __nonzero__(self):
+    def __bool__(self):
         if not self.name:
             return False
 
@@ -129,6 +129,10 @@ class ImageCacheFile(BaseIKFile, ImageFile):
         existence_required.send(sender=self, file=self)
         return self.cachefile_backend.exists(self)
 
+    def __nonzero__(self):
+        # Python 2 compatibility
+        return self.__bool__()
+
 
 class LazyImageCacheFile(SimpleLazyObject):
     def __init__(self, generator_id, *args, **kwargs):
diff --git a/imagekit/cachefiles/strategies.py b/imagekit/cachefiles/strategies.py
index fba6a0f..0d11dae 100644
--- a/imagekit/cachefiles/strategies.py
+++ b/imagekit/cachefiles/strategies.py
@@ -1,4 +1,7 @@
+import six
+
 from django.utils.functional import LazyObject
+from ..lib import force_text
 from ..utils import get_singleton
 
 
@@ -35,7 +38,7 @@ class DictStrategy(object):
 
 class StrategyWrapper(LazyObject):
     def __init__(self, strategy):
-        if isinstance(strategy, basestring):
+        if isinstance(strategy, six.string_types):
             strategy = get_singleton(strategy, 'cache file strategy')
         elif isinstance(strategy, dict):
             strategy = DictStrategy(strategy)
@@ -50,7 +53,7 @@ class StrategyWrapper(LazyObject):
         self._wrapped = state['_wrapped']
 
     def __unicode__(self):
-        return unicode(self._wrapped)
+        return force_text(self._wrapped)
 
     def __str__(self):
         return str(self._wrapped)
diff --git a/imagekit/files.py b/imagekit/files.py
index fb4375c..e717888 100644
--- a/imagekit/files.py
+++ b/imagekit/files.py
@@ -1,6 +1,9 @@
-from django.core.files.base import File, ContentFile
-from django.utils.encoding import smart_str, smart_unicode
+from __future__ import unicode_literals
 import os
+
+from django.core.files.base import File, ContentFile
+from django.utils.encoding import smart_str
+from .lib import smart_text
 from .utils import format_to_mimetype, extension_to_mimetype
 
 
@@ -92,4 +95,5 @@ class IKContentFile(ContentFile):
         return smart_str(self.file.name or '')
 
     def __unicode__(self):
-        return smart_unicode(self.file.name or u'')
+        # Python 2
+        return smart_text(self.file.name or '')
diff --git a/imagekit/hashers.py b/imagekit/hashers.py
index 4231fa5..12825bd 100644
--- a/imagekit/hashers.py
+++ b/imagekit/hashers.py
@@ -1,12 +1,16 @@
 from copy import copy
 from hashlib import md5
-from pickle import Pickler, MARK, DICT
-from types import DictionaryType
+from pickle import MARK, DICT
+try:
+    from pickle import _Pickler
+except ImportError:
+    # Python 2 compatible
+    from pickle import Pickler as _Pickler
 from .lib import StringIO
 
 
-class CanonicalizingPickler(Pickler):
-    dispatch = copy(Pickler.dispatch)
+class CanonicalizingPickler(_Pickler):
+    dispatch = copy(_Pickler.dispatch)
 
     def save_set(self, obj):
         rv = obj.__reduce_ex__(0)
@@ -20,9 +24,9 @@ class CanonicalizingPickler(Pickler):
         write(MARK + DICT)
 
         self.memoize(obj)
-        self._batch_setitems(sorted(obj.iteritems()))
+        self._batch_setitems(sorted(obj.items()))
 
-    dispatch[DictionaryType] = save_dict
+    dispatch[dict] = save_dict
 
 
 def pickle(obj):
diff --git a/imagekit/lib.py b/imagekit/lib.py
index 6da2bfb..4fe2c05 100644
--- a/imagekit/lib.py
+++ b/imagekit/lib.py
@@ -19,9 +19,12 @@ except ImportError:
         raise ImportError('ImageKit was unable to import the Python Imaging Library. Please confirm it`s installed and available on your current Python path.')
 
 try:
-    from cStringIO import StringIO
-except ImportError:
-    from StringIO import StringIO
+    from io import BytesIO as StringIO
+except:
+    try:
+        from cStringIO import StringIO
+    except ImportError:
+        from StringIO import StringIO
 
 try:
     from logging import NullHandler
@@ -31,3 +34,17 @@ except ImportError:
     class NullHandler(Handler):
         def emit(self, record):
             pass
+
+# Try to import `force_text` available from Django 1.5
+# This function will replace `unicode` used in the code
+# If Django version is under 1.5 then use `force_unicde`
+# It is used for compatibility between Python 2 and Python 3
+# NOTE: I'm not sure if this is the right place. Maybe this can be in `utils`.
+try:
+    from django.utils.encoding import force_text, smart_text
+except ImportError:
+    # Django < 1.5
+    from django.utils.encoding import force_unicode as force_text, smart_unicode as smart_text
+
+__all__ = ['Image', 'ImageColor', 'ImageChops', 'ImageEnhance', 'ImageFile', 'ImageFilter',
+           'ImageDraw', 'ImageStat', 'StringIO', 'NullHandler', 'force_text', 'smart_text']
diff --git a/imagekit/models/fields/__init__.py b/imagekit/models/fields/__init__.py
index 91c6252..e2ccf26 100644
--- a/imagekit/models/fields/__init__.py
+++ b/imagekit/models/fields/__init__.py
@@ -1,3 +1,5 @@
+from __future__ import unicode_literals
+
 from django.db import models
 from .files import ProcessedImageFieldFile
 from .utils import ImageSpecFileDescriptor
@@ -13,7 +15,7 @@ class SpecHostField(SpecHost):
         # Generate a spec_id to register the spec with. The default spec id is
         # "<app>:<model>_<field>"
         if not spec_id:
-            spec_id = (u'%s:%s:%s' % (cls._meta.app_label,
+            spec_id = ('%s:%s:%s' % (cls._meta.app_label,
                             cls._meta.object_name, name)).lower()
 
         # Register the spec with the id. This allows specs to be overridden
diff --git a/imagekit/templatetags/imagekit.py b/imagekit/templatetags/imagekit.py
index 2df5b4d..25c2cca 100644
--- a/imagekit/templatetags/imagekit.py
+++ b/imagekit/templatetags/imagekit.py
@@ -1,9 +1,13 @@
+from __future__ import unicode_literals
+
 from django import template
 from django.utils.html import escape
 from django.utils.safestring import mark_safe
+
 from .compat import parse_bits
 from ..cachefiles import ImageCacheFile
 from ..registry import generator_registry
+from ..lib import force_text
 
 
 register = template.Library()
@@ -40,7 +44,7 @@ class GenerateImageAssignmentNode(template.Node):
         self._variable_name = variable_name
 
     def get_variable_name(self, context):
-        return unicode(self._variable_name)
+        return force_text(self._variable_name)
 
     def render(self, context):
         variable_name = self.get_variable_name(context)
@@ -70,7 +74,7 @@ class GenerateImageTagNode(template.Node):
         attrs['src'] = file.url
         attr_str = ' '.join('%s="%s"' % (escape(k), escape(v)) for k, v in
                 attrs.items())
-        return mark_safe(u'<img %s />' % attr_str)
+        return mark_safe('<img %s />' % attr_str)
 
 
 class ThumbnailAssignmentNode(template.Node):
@@ -83,7 +87,7 @@ class ThumbnailAssignmentNode(template.Node):
         self._generator_kwargs = generator_kwargs
 
     def get_variable_name(self, context):
-        return unicode(self._variable_name)
+        return force_text(self._variable_name)
 
     def render(self, context):
         variable_name = self.get_variable_name(context)
@@ -131,7 +135,7 @@ class ThumbnailImageTagNode(template.Node):
         attrs['src'] = file.url
         attr_str = ' '.join('%s="%s"' % (escape(k), escape(v)) for k, v in
                 attrs.items())
-        return mark_safe(u'<img %s />' % attr_str)
+        return mark_safe('<img %s />' % attr_str)
 
 
 def parse_ik_tag_bits(parser, bits):
diff --git a/imagekit/utils.py b/imagekit/utils.py
index 13bd843..598be43 100644
--- a/imagekit/utils.py
+++ b/imagekit/utils.py
@@ -1,3 +1,4 @@
+from __future__ import unicode_literals
 import logging
 from tempfile import NamedTemporaryFile
 
@@ -11,7 +12,7 @@ import re
 from .lib import NullHandler
 
 
-bad_memcached_key_chars = re.compile(ur'[\u0000-\u001f\s]+')
+bad_memcached_key_chars = re.compile(r'[\u0000-\u001f\s]+')
 
 _autodiscovered = False
 
@@ -32,7 +33,7 @@ def get_by_qname(path, desc):
     module, objname = path[:dot], path[dot + 1:]
     try:
         mod = import_module(module)
-    except ImportError, e:
+    except ImportError as e:
         raise ImproperlyConfigured('Error importing %s module %s: "%s"' %
                 (desc, module, e))
     try:
diff --git a/setup.py b/setup.py
index da959a0..2f30679 100644
--- a/setup.py
+++ b/setup.py
@@ -19,10 +19,12 @@ if 'publish' in sys.argv:
 
 read = lambda filepath: codecs.open(filepath, 'r', 'utf-8').read()
 
+def exec_file(filepath, globalz=None, localz=None):
+        exec(read(filepath), globalz, localz)
 
 # Load package meta from the pkgmeta module without loading imagekit.
 pkgmeta = {}
-execfile(os.path.join(os.path.dirname(__file__),
+exec_file(os.path.join(os.path.dirname(__file__),
          'imagekit', 'pkgmeta.py'), pkgmeta)
 
 
@@ -51,6 +53,7 @@ setup(
     install_requires=[
         'django-appconf>=0.5',
         'pilkit>=0.2.0',
+        'six',
     ],
     extras_require={
         'async': ['django-celery>=3.0'],
@@ -62,9 +65,10 @@ setup(
         'Intended Audience :: Developers',
         'License :: OSI Approved :: BSD License',
         'Operating System :: OS Independent',
-        'Programming Language :: Python :: 2.5',
         'Programming Language :: Python :: 2.6',
         'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 3.2',
+        'Programming Language :: Python :: 3.3',
         'Topic :: Utilities'
     ],
 )

From 183efabca7573c29908f38de160dd86074a2be2c Mon Sep 17 00:00:00 2001
From: Matthew Tretter <m@tthewwithanm.com>
Date: Sun, 1 Sep 2013 21:55:37 -0400
Subject: [PATCH 02/12] Delay Django import until needed

---
 imagekit/importers.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/imagekit/importers.py b/imagekit/importers.py
index cddcd83..b2896cf 100644
--- a/imagekit/importers.py
+++ b/imagekit/importers.py
@@ -1,4 +1,3 @@
-from django.utils.importlib import import_module
 import re
 import sys
 
@@ -22,6 +21,7 @@ class ProcessorImporter(object):
         if name in sys.modules:
             return sys.modules[name]
 
+        from django.utils.importlib import import_module
         new_name = self.pattern.sub(r'pilkit.processors\1', name)
         return import_module(new_name)
 

From 3732b2ee099989ed46e264f031b9b47c414cf6c6 Mon Sep 17 00:00:00 2001
From: Matthew Tretter <m@tthewwithanm.com>
Date: Sun, 1 Sep 2013 21:55:58 -0400
Subject: [PATCH 03/12] Insert importer at beginning of list

---
 imagekit/importers.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/imagekit/importers.py b/imagekit/importers.py
index b2896cf..67d2b51 100644
--- a/imagekit/importers.py
+++ b/imagekit/importers.py
@@ -26,4 +26,4 @@ class ProcessorImporter(object):
         return import_module(new_name)
 
 
-sys.meta_path.append(ProcessorImporter())
+sys.meta_path.insert(0, ProcessorImporter())

From 2e4d435f4f9c7f582ef9db4b00941bec4a87cea6 Mon Sep 17 00:00:00 2001
From: Matthew Tretter <m@tthewwithanm.com>
Date: Sun, 1 Sep 2013 21:56:28 -0400
Subject: [PATCH 04/12] Test for Python 3

---
 setup.py |  6 +++---
 tox.ini  | 12 ++++++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/setup.py b/setup.py
index 2f30679..c54c041 100644
--- a/setup.py
+++ b/setup.py
@@ -44,9 +44,9 @@ setup(
     include_package_data=True,
     tests_require=[
         'beautifulsoup4==4.1.3',
-        'nose==1.2.1',
-        'nose-progressive==1.3',
-        'django-nose==1.1',
+        'nose==1.3.0',
+        'nose-progressive==1.5',
+        'django-nose==1.2',
         'Pillow<3.0',
     ],
     test_suite='testrunner.run_tests',
diff --git a/tox.ini b/tox.ini
index 46ca387..1dc2b41 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,11 +1,23 @@
 [tox]
 envlist =
+    py33-django15,
+    py32-django15,
     py27-django15, py27-django14, py27-django13, py27-django12,
     py26-django15, py26-django14, py26-django13, py26-django12
 
 [testenv]
 commands = python setup.py test
 
+[testenv:py33-django15]
+basepython = python3.3
+deps =
+    Django>=1.5,<1.6
+
+[testenv:py32-django15]
+basepython = python3.2
+deps =
+    Django>=1.5,<1.6
+
 [testenv:py27-django15]
 basepython = python2.7
 deps =

From bf1b45c943715efd8eef2e73ef77d6681da5658f Mon Sep 17 00:00:00 2001
From: Matthew Tretter <m@tthewwithanm.com>
Date: Sun, 1 Sep 2013 21:56:42 -0400
Subject: [PATCH 05/12] Add module to sys.modules

---
 imagekit/importers.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/imagekit/importers.py b/imagekit/importers.py
index 67d2b51..87ba2b6 100644
--- a/imagekit/importers.py
+++ b/imagekit/importers.py
@@ -23,7 +23,9 @@ class ProcessorImporter(object):
 
         from django.utils.importlib import import_module
         new_name = self.pattern.sub(r'pilkit.processors\1', name)
-        return import_module(new_name)
+        mod = import_module(new_name)
+        sys.modules[name] = mod
+        return mod
 
 
 sys.meta_path.insert(0, ProcessorImporter())

From fb947b19374244bc28dbe09100dfd0e628b16ad4 Mon Sep 17 00:00:00 2001
From: Venelin Stoykov <vkstoykov@gmail.com>
Date: Sat, 14 Dec 2013 18:56:47 +0200
Subject: [PATCH 06/12] Fix sanitizing cache key under Python 3

---
 imagekit/utils.py        | 10 +++++++---
 tests/test_cachefiles.py |  6 +++++-
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/imagekit/utils.py b/imagekit/utils.py
index 598be43..baaf234 100644
--- a/imagekit/utils.py
+++ b/imagekit/utils.py
@@ -1,14 +1,18 @@
 from __future__ import unicode_literals
 import logging
+import re
 from tempfile import NamedTemporaryFile
+from hashlib import md5
 
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.core.files import File
 from django.utils.importlib import import_module
-from hashlib import md5
+try:
+    from django.utils.encoding import force_bytes
+except ImportError:
+    from django.utils.encoding import smart_str as force_bytes
 from pilkit.utils import *
-import re
 from .lib import NullHandler
 
 
@@ -148,7 +152,7 @@ def sanitize_cache_key(key):
         # The also can't be > 250 chars long. Since we don't know what the
         # user's cache ``KEY_FUNCTION`` setting is like, we'll limit it to 200.
         if len(new_key) >= 200:
-            new_key = '%s:%s' % (new_key[:200-33], md5(key).hexdigest())
+            new_key = '%s:%s' % (new_key[:200-33], md5(force_bytes(key)).hexdigest())
 
         key = new_key
     return key
diff --git a/tests/test_cachefiles.py b/tests/test_cachefiles.py
index 4338a82..ba250fb 100644
--- a/tests/test_cachefiles.py
+++ b/tests/test_cachefiles.py
@@ -1,4 +1,8 @@
 from django.conf import settings
+try:
+    from django.utils.encoding import force_bytes
+except ImportError:
+    from django.utils.encoding import smart_str as force_bytes
 from hashlib import md5
 from imagekit.cachefiles import ImageCacheFile, LazyImageCacheFile
 from imagekit.cachefiles.backends import Simple
@@ -73,7 +77,7 @@ def test_memcached_cache_key():
     eq_(backend.get_key(file), '%s%s:%s' % (
         settings.IMAGEKIT_CACHE_PREFIX,
         '1' * (200 - len(':') - 32 - len(settings.IMAGEKIT_CACHE_PREFIX)),
-        md5('%s%s-state' % (settings.IMAGEKIT_CACHE_PREFIX, filename)).hexdigest()))
+        md5(force_bytes('%s%s-state' % (settings.IMAGEKIT_CACHE_PREFIX, filename))).hexdigest()))
 
 
 def test_lazyfile_stringification():

From c1e16696b14a71049985d6a49a4005a2cd93c593 Mon Sep 17 00:00:00 2001
From: Matthew Dapena-Tretter <m@tthewwithanm.com>
Date: Sat, 14 Dec 2013 12:54:26 -0500
Subject: [PATCH 07/12] Don't use a raw string with \u escapes

Apparently, Python 3.2 doesn't process these in raw strings.
See https://mail.python.org/pipermail/python-list/2012-May/624756.html
and https://mail.python.org/pipermail/python-dev/2007-May/073042.html
---
 imagekit/utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/imagekit/utils.py b/imagekit/utils.py
index baaf234..c889e28 100644
--- a/imagekit/utils.py
+++ b/imagekit/utils.py
@@ -16,7 +16,7 @@ from pilkit.utils import *
 from .lib import NullHandler
 
 
-bad_memcached_key_chars = re.compile(r'[\u0000-\u001f\s]+')
+bad_memcached_key_chars = re.compile('[\u0000-\u001f\\s]+')
 
 _autodiscovered = False
 

From 87983c5e6de8030737803791670284ae0bd410ef Mon Sep 17 00:00:00 2001
From: Matthew Dapena-Tretter <m@tthewwithanm.com>
Date: Sat, 14 Dec 2013 13:02:21 -0500
Subject: [PATCH 08/12] Move force_bytes into lib module

---
 imagekit/lib.py   | 11 +++++++----
 imagekit/utils.py |  6 +-----
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/imagekit/lib.py b/imagekit/lib.py
index 4fe2c05..12460c9 100644
--- a/imagekit/lib.py
+++ b/imagekit/lib.py
@@ -41,10 +41,13 @@ except ImportError:
 # It is used for compatibility between Python 2 and Python 3
 # NOTE: I'm not sure if this is the right place. Maybe this can be in `utils`.
 try:
-    from django.utils.encoding import force_text, smart_text
+    from django.utils.encoding import force_text, force_bytes, smart_text
 except ImportError:
     # Django < 1.5
-    from django.utils.encoding import force_unicode as force_text, smart_unicode as smart_text
+    from django.utils.encoding import (force_unicode as force_text,
+                                       smart_str as force_bytes,
+                                       smart_unicode as smart_text)
 
-__all__ = ['Image', 'ImageColor', 'ImageChops', 'ImageEnhance', 'ImageFile', 'ImageFilter',
-           'ImageDraw', 'ImageStat', 'StringIO', 'NullHandler', 'force_text', 'smart_text']
+__all__ = ['Image', 'ImageColor', 'ImageChops', 'ImageEnhance', 'ImageFile',
+           'ImageFilter', 'ImageDraw', 'ImageStat', 'StringIO', 'NullHandler',
+           'force_text', 'force_bytes', 'smart_text']
diff --git a/imagekit/utils.py b/imagekit/utils.py
index c889e28..0973d35 100644
--- a/imagekit/utils.py
+++ b/imagekit/utils.py
@@ -8,12 +8,8 @@ from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.core.files import File
 from django.utils.importlib import import_module
-try:
-    from django.utils.encoding import force_bytes
-except ImportError:
-    from django.utils.encoding import smart_str as force_bytes
 from pilkit.utils import *
-from .lib import NullHandler
+from .lib import NullHandler, force_bytes
 
 
 bad_memcached_key_chars = re.compile('[\u0000-\u001f\\s]+')

From 45f10075b644dc00f3a274223cc1d9aacd1af24b Mon Sep 17 00:00:00 2001
From: Matthew Dapena-Tretter <m@tthewwithanm.com>
Date: Sat, 14 Dec 2013 13:03:02 -0500
Subject: [PATCH 09/12] Remove @vstoykov's note. Seems like the right place to
 me (:

---
 imagekit/lib.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/imagekit/lib.py b/imagekit/lib.py
index 12460c9..5a4240b 100644
--- a/imagekit/lib.py
+++ b/imagekit/lib.py
@@ -39,7 +39,6 @@ except ImportError:
 # This function will replace `unicode` used in the code
 # If Django version is under 1.5 then use `force_unicde`
 # It is used for compatibility between Python 2 and Python 3
-# NOTE: I'm not sure if this is the right place. Maybe this can be in `utils`.
 try:
     from django.utils.encoding import force_text, force_bytes, smart_text
 except ImportError:

From 8a600d30b32aee0dd95ff28c02c6e211e6749160 Mon Sep 17 00:00:00 2001
From: Venelin Stoykov <vkstoykov@gmail.com>
Date: Sun, 15 Dec 2013 01:58:22 +0200
Subject: [PATCH 10/12] Use force_bytes from imagekit.lib in test_cachefiles

---
 tests/test_cachefiles.py | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/tests/test_cachefiles.py b/tests/test_cachefiles.py
index ba250fb..8a93e71 100644
--- a/tests/test_cachefiles.py
+++ b/tests/test_cachefiles.py
@@ -1,11 +1,8 @@
 from django.conf import settings
-try:
-    from django.utils.encoding import force_bytes
-except ImportError:
-    from django.utils.encoding import smart_str as force_bytes
 from hashlib import md5
 from imagekit.cachefiles import ImageCacheFile, LazyImageCacheFile
 from imagekit.cachefiles.backends import Simple
+from imagekit.lib import force_bytes
 from nose.tools import raises, eq_
 from .imagegenerators import TestSpec
 from .utils import (assert_file_is_truthy, assert_file_is_falsy,

From 26aa19eeef7cbc679f87f7482651386df47d7410 Mon Sep 17 00:00:00 2001
From: Venelin Stoykov <vkstoykov@gmail.com>
Date: Sun, 15 Dec 2013 02:34:25 +0200
Subject: [PATCH 11/12] Improve logic of contributing ImageSpecFields to Models

- If `source` is defined then register source group immediately
- If `source` is not defined then create a signal handler and attach it to
`class_prepared` signal which will see if there is only one ImageField in
the given model.

This will fix problems coused in Python 3 about using ImageSpecField
without providing a `source`.
---
 imagekit/models/fields/__init__.py | 51 +++++++++++++++++++-----------
 1 file changed, 32 insertions(+), 19 deletions(-)

diff --git a/imagekit/models/fields/__init__.py b/imagekit/models/fields/__init__.py
index e2ccf26..61a7dd3 100644
--- a/imagekit/models/fields/__init__.py
+++ b/imagekit/models/fields/__init__.py
@@ -1,6 +1,8 @@
 from __future__ import unicode_literals
 
 from django.db import models
+from django.db.models.signals import class_prepared
+from django.dispatch import receiver
 from .files import ProcessedImageFieldFile
 from .utils import ImageSpecFileDescriptor
 from ...specs import SpecHost
@@ -46,27 +48,38 @@ class ImageSpecField(SpecHostField):
 
     def contribute_to_class(self, cls, name):
         # If the source field name isn't defined, figure it out.
-        source = self.source
-        if not source:
-            image_fields = [f.attname for f in cls._meta.fields if
-                            isinstance(f, models.ImageField)]
-            if len(image_fields) == 0:
-                raise Exception(
-                    '%s does not define any ImageFields, so your %s'
-                    ' ImageSpecField has no image to act on.' %
-                    (cls.__name__, name))
-            elif len(image_fields) > 1:
-                raise Exception(
-                    '%s defines multiple ImageFields, but you have not'
-                    ' specified a source for your %s ImageSpecField.' %
-                    (cls.__name__, name))
-            source = image_fields[0]
 
-        setattr(cls, name, ImageSpecFileDescriptor(self, name, source))
-        self._set_spec_id(cls, name)
+        def register_source_group(source):
+            setattr(cls, name, ImageSpecFileDescriptor(self, name, source))
+            self._set_spec_id(cls, name)
+
+            # Add the model and field as a source for this spec id
+            register.source_group(self.spec_id, ImageFieldSourceGroup(cls, source))
+
+        if self.source:
+            register_source_group(self.source)
+        else:
+            # The source argument is not defined
+            # Then we need to see if there is only one ImageField in that model
+            # But we need to do that after full model initialization
+
+            @receiver(class_prepared, sender=cls, weak=False)
+            def handle_model_preparation(sender, **kwargs):
+
+                image_fields = [f.attname for f in cls._meta.fields if
+                                isinstance(f, models.ImageField)]
+                if len(image_fields) == 0:
+                    raise Exception(
+                        '%s does not define any ImageFields, so your %s'
+                        ' ImageSpecField has no image to act on.' %
+                        (cls.__name__, name))
+                elif len(image_fields) > 1:
+                    raise Exception(
+                        '%s defines multiple ImageFields, but you have not'
+                        ' specified a source for your %s ImageSpecField.' %
+                        (cls.__name__, name))
+                register_source_group(image_fields[0])
 
-        # Add the model and field as a source for this spec id
-        register.source_group(self.spec_id, ImageFieldSourceGroup(cls, source))
 
 
 class ProcessedImageField(models.ImageField, SpecHostField):

From 3667c09d8221681d68e9ad93504d3380b61f889b Mon Sep 17 00:00:00 2001
From: Venelin Stoykov <vkstoykov@gmail.com>
Date: Mon, 16 Dec 2013 22:38:05 +0200
Subject: [PATCH 12/12] Add Venelin Stoykov to AUTHORS

---
 AUTHORS | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/AUTHORS b/AUTHORS
index 255827b..6f4c238 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -28,6 +28,7 @@ Contributors
 * `Jannis Leidel`_
 * `Sean Bell`_
 * `Saul Shanabrook`_
+* `Venelin Stoykov`_
 
 .. _Justin Driscoll: http://github.com/jdriscoll
 .. _HZDG: http://hzdg.com
@@ -49,3 +50,4 @@ Contributors
 .. _Jannis Leidel: https://github.com/jezdez
 .. _Sean Bell: https://github.com/seanbell
 .. _Saul Shanabrook: https://github.com/saulshanabrook
+.. _Venelin Stoykov: https://github.com/vstoykov