import os
import random
import shutil
import zipfile
from datetime import datetime
from inspect import isclass
from django.db import models
from django.db.models.signals import post_init
from django.conf import settings
from django.core.files.base import ContentFile
from django.core.urlresolvers import reverse
from django.template.defaultfilters import slugify
from django.utils.functional import curry
from django.utils.translation import ugettext_lazy as _
# Required PIL classes may or may not be available from the root namespace
# depending on the installation method used.
try:
import Image
import ImageFile
import ImageFilter
import ImageEnhance
except ImportError:
try:
from PIL import Image
from PIL import ImageFile
from PIL import ImageFilter
from PIL import ImageEnhance
except ImportError:
raise ImportError('Photologue was unable to import the Python Imaging Library. Please confirm it`s installed and available on your current Python path.')
# attempt to load the django-tagging TagField from default location,
# otherwise we substitude a dummy TagField.
try:
from tagging.fields import TagField
tagfield_help_text = _('Separate tags with spaces, put quotes around multiple-word tags.')
except ImportError:
class TagField(models.CharField):
def __init__(self, **kwargs):
default_kwargs = {'max_length': 255, 'blank': True}
default_kwargs.update(kwargs)
super(TagField, self).__init__(**default_kwargs)
def get_internal_type(self):
return 'CharField'
tagfield_help_text = _('Django-tagging was not found, tags will be treated as plain text.')
from utils import EXIF
from utils.reflection import add_reflection
from utils.watermark import apply_watermark
# Path to sample image
SAMPLE_IMAGE_PATH = getattr(settings, 'SAMPLE_IMAGE_PATH', os.path.join(os.path.dirname(__file__), 'res', 'sample.jpg')) # os.path.join(settings.PROJECT_PATH, 'photologue', 'res', 'sample.jpg'
# Modify image file buffer size.
ImageFile.MAXBLOCK = getattr(settings, 'PHOTOLOGUE_MAXBLOCK', 256 * 2 ** 10)
# Photologue image path relative to media root
PHOTOLOGUE_DIR = getattr(settings, 'PHOTOLOGUE_DIR', 'photologue')
# Look for user function to define file paths
PHOTOLOGUE_PATH = getattr(settings, 'PHOTOLOGUE_PATH', None)
if PHOTOLOGUE_PATH is not None:
if callable(PHOTOLOGUE_PATH):
get_storage_path = PHOTOLOGUE_PATH
else:
parts = PHOTOLOGUE_PATH.split('.')
module_name = '.'.join(parts[:-1])
module = __import__(module_name)
get_storage_path = getattr(module, parts[-1])
else:
def get_storage_path(instance, filename):
return os.path.join(PHOTOLOGUE_DIR, 'photos', filename)
# Quality options for JPEG images
JPEG_QUALITY_CHOICES = (
(30, _('Very Low')),
(40, _('Low')),
(50, _('Medium-Low')),
(60, _('Medium')),
(70, _('Medium-High')),
(80, _('High')),
(90, _('Very High')),
)
# choices for new crop_anchor field in Photo
CROP_ANCHOR_CHOICES = (
('top', _('Top')),
('right', _('Right')),
('bottom', _('Bottom')),
('left', _('Left')),
('center', _('Center (Default)')),
)
IMAGE_TRANSPOSE_CHOICES = (
('FLIP_LEFT_RIGHT', _('Flip left to right')),
('FLIP_TOP_BOTTOM', _('Flip top to bottom')),
('ROTATE_90', _('Rotate 90 degrees counter-clockwise')),
('ROTATE_270', _('Rotate 90 degrees clockwise')),
('ROTATE_180', _('Rotate 180 degrees')),
)
WATERMARK_STYLE_CHOICES = (
('tile', _('Tile')),
('scale', _('Scale')),
)
# Prepare a list of image filters
filter_names = []
for n in dir(ImageFilter):
klass = getattr(ImageFilter, n)
if isclass(klass) and issubclass(klass, ImageFilter.BuiltinFilter) and \
hasattr(klass, 'name'):
filter_names.append(klass.__name__)
IMAGE_FILTERS_HELP_TEXT = _('Chain multiple filters using the following pattern "FILTER_ONE->FILTER_TWO->FILTER_THREE". Image filters will be applied in order. The following filters are available: %s.' % (', '.join(filter_names)))
class Gallery(models.Model):
date_added = models.DateTimeField(_('date published'), default=datetime.now)
title = models.CharField(_('title'), max_length=100, unique=True)
title_slug = models.SlugField(_('title slug'), unique=True,
help_text=_('A "slug" is a unique URL-friendly title for an object.'))
description = models.TextField(_('description'), blank=True)
is_public = models.BooleanField(_('is public'), default=True,
help_text=_('Public galleries will be displayed in the default views.'))
photos = models.ManyToManyField('Photo', related_name='galleries', verbose_name=_('photos'),
null=True, blank=True)
tags = TagField(help_text=tagfield_help_text, verbose_name=_('tags'))
class Meta:
ordering = ['-date_added']
get_latest_by = 'date_added'
verbose_name = _('gallery')
verbose_name_plural = _('galleries')
def __unicode__(self):
return self.title
def __str__(self):
return self.__unicode__()
def get_absolute_url(self):
return reverse('pl-gallery', args=[self.title_slug])
def latest(self, limit=0, public=True):
if limit == 0:
limit = self.photo_count()
if public:
return self.public()[:limit]
else:
return self.photos.all()[:limit]
def sample(self, count=0, public=True):
if count == 0 or count > self.photo_count():
count = self.photo_count()
if public:
photo_set = self.public()
else:
photo_set = self.photos.all()
return random.sample(photo_set, count)
def photo_count(self, public=True):
if public:
return self.public().count()
else:
return self.photos.all().count()
photo_count.short_description = _('count')
def public(self):
return self.photos.filter(is_public=True)
class GalleryUpload(models.Model):
zip_file = models.FileField(_('images file (.zip)'), upload_to=PHOTOLOGUE_DIR+"/temp",
help_text=_('Select a .zip file of images to upload into a new Gallery.'))
gallery = models.ForeignKey(Gallery, null=True, blank=True, help_text=_('Select a gallery to add these images to. leave this empty to create a new gallery from the supplied title.'))
title = models.CharField(_('title'), max_length=75, help_text=_('All photos in the gallery will be given a title made up of the gallery title + a sequential number.'))
caption = models.TextField(_('caption'), blank=True, help_text=_('Caption will be added to all photos.'))
description = models.TextField(_('description'), blank=True, help_text=_('A description of this Gallery.'))
is_public = models.BooleanField(_('is public'), default=True, help_text=_('Uncheck this to make the uploaded gallery and included photographs private.'))
tags = models.CharField(max_length=255, blank=True, help_text=tagfield_help_text, verbose_name=_('tags'))
class Meta:
verbose_name = _('gallery upload')
verbose_name_plural = _('gallery uploads')
def save(self, *args, **kwargs):
super(GalleryUpload, self).save(*args, **kwargs)
gallery = self.process_zipfile()
super(GalleryUpload, self).delete()
return gallery
def process_zipfile(self):
if os.path.isfile(self.zip_file.path):
# TODO: implement try-except here
zip = zipfile.ZipFile(self.zip_file.path)
bad_file = zip.testzip()
if bad_file:
raise Exception('"%s" in the .zip archive is corrupt.' % bad_file)
count = 1
if self.gallery:
gallery = self.gallery
else:
gallery = Gallery.objects.create(title=self.title,
title_slug=slugify(self.title),
description=self.description,
is_public=self.is_public,
tags=self.tags)
from cStringIO import StringIO
for filename in zip.namelist():
if filename.startswith('__'): # do not process meta files
continue
data = zip.read(filename)
if len(data):
try:
# the following is taken from django.newforms.fields.ImageField:
# load() is the only method that can spot a truncated JPEG,
# but it cannot be called sanely after verify()
trial_image = Image.open(StringIO(data))
trial_image.load()
# verify() is the only method that can spot a corrupt PNG,
# but it must be called immediately after the constructor
trial_image = Image.open(StringIO(data))
trial_image.verify()
except Exception:
# if a "bad" file is found we just skip it.
continue
while 1:
title = ' '.join([self.title, str(count)])
slug = slugify(title)
try:
p = Photo.objects.get(title_slug=slug)
except Photo.DoesNotExist:
photo = Photo(title=title,
title_slug=slug,
caption=self.caption,
is_public=self.is_public,
tags=self.tags)
photo.image.save(filename, ContentFile(data))
gallery.photos.add(photo)
count = count + 1
break
count = count + 1
zip.close()
return gallery
class ImageModel(models.Model):
image = models.ImageField(_('image'), upload_to=get_storage_path)
date_taken = models.DateTimeField(_('date taken'), null=True, blank=True, editable=False)
view_count = models.PositiveIntegerField(default=0, editable=False)
crop_from = models.CharField(_('crop from'), blank=True, max_length=10, default='center', choices=CROP_ANCHOR_CHOICES)
effect = models.ForeignKey('PhotoEffect', null=True, blank=True, related_name="%(class)s_related", verbose_name=_('effect'))
class Meta:
abstract = True
@property
def EXIF(self):
try:
return EXIF.process_file(open(self.image.path, 'rb'))
except:
try:
return EXIF.process_file(open(self.image.path, 'rb'), details=False)
except:
return {}
def admin_thumbnail(self):
func = getattr(self, 'get_admin_thumbnail_url', None)
if func is None:
return _('An "admin_thumbnail" photo size has not been defined.')
else:
if hasattr(self, 'get_absolute_url'):
return u'<a href="%s"><img src="%s"></a>' % \
(self.get_absolute_url(), func())
else:
return u'<a href="%s"><img src="%s"></a>' % \
(self.image.url, func())
admin_thumbnail.short_description = _('Thumbnail')
admin_thumbnail.allow_tags = True
def cache_path(self):
return os.path.join(os.path.dirname(self.image.path), "cache")
def cache_url(self):
return '/'.join([os.path.dirname(self.image.url), "cache"])
def image_filename(self):
return os.path.basename(self.image.path)
def _get_filename_for_size(self, size):
size = getattr(size, 'name', size)
base, ext = os.path.splitext(self.image_filename())
return ''.join([base, '_', size, ext])
def _get_SIZE_photosize(self, size):
return PhotoSizeCache().sizes.get(size)
def _get_SIZE_size(self, size):
photosize = PhotoSizeCache().sizes.get(size)
if not self.size_exists(photosize):
self.create_size(photosize)
return Image.open(self._get_SIZE_filename(size)).size
def _get_SIZE_url(self, size):
photosize = PhotoSizeCache().sizes.get(size)
if not self.size_exists(photosize):
self.create_size(photosize)
if photosize.increment_count:
self.increment_count()
return '/'.join([self.cache_url(), self._get_filename_for_size(photosize.name)])
def _get_SIZE_filename(self, size):
photosize = PhotoSizeCache().sizes.get(size)
return os.path.join(self.cache_path(),
self._get_filename_for_size(photosize.name))
def increment_count(self):
self.view_count += 1
models.Model.save(self)
def add_accessor_methods(self, *args, **kwargs):
for size in PhotoSizeCache().sizes.keys():
setattr(self, 'get_%s_size' % size,
curry(self._get_SIZE_size, size=size))
setattr(self, 'get_%s_photosize' % size,
curry(self._get_SIZE_photosize, size=size))
setattr(self, 'get_%s_url' % size,
curry(self._get_SIZE_url, size=size))
setattr(self, 'get_%s_filename' % size,
curry(self._get_SIZE_filename, size=size))
def size_exists(self, photosize):
func = getattr(self, "get_%s_filename" % photosize.name, None)
if func is not None:
if os.path.isfile(func()):
return True
return False
def resize_image(self, im, photosize):
cur_width, cur_height = im.size
new_width, new_height = photosize.size
if photosize.crop:
ratio = max(float(new_width)/cur_width,float(new_height)/cur_height)
x = (cur_width * ratio)
y = (cur_height * ratio)
xd = abs(new_width - x)
yd = abs(new_height - y)
x_diff = int(xd / 2)
y_diff = int(yd / 2)
if self.crop_from == 'top':
box = (int(x_diff), 0, int(x_diff+new_width), new_height)
elif self.crop_from == 'left':
box = (0, int(y_diff), new_width, int(y_diff+new_height))
elif self.crop_from == 'bottom':
box = (int(x_diff), int(yd), int(x_diff+new_width), int(y)) # y - yd = new_height
elif self.crop_from == 'right':
box = (int(xd), int(y_diff), int(x), int(y_diff+new_height)) # x - xd = new_width
else:
box = (int(x_diff), int(y_diff), int(x_diff+new_width), int(y_diff+new_height))
im = im.resize((int(x), int(y)), Image.ANTIALIAS).crop(box)
else:
if not new_width == 0 and not new_height == 0:
ratio = min(float(new_width)/cur_width,
float(new_height)/cur_height)
else:
if new_width == 0:
ratio = float(new_height)/cur_height
else:
ratio = float(new_width)/cur_width
new_dimensions = (int(round(cur_width*ratio)),
int(round(cur_height*ratio)))
if new_dimensions[0] > cur_width or \
new_dimensions[1] > cur_height:
if not photosize.upscale:
return im
im = im.resize(new_dimensions, Image.ANTIALIAS)
return im
def create_size(self, photosize):
if self.size_exists(photosize):
return
if not os.path.isdir(self.cache_path()):
os.makedirs(self.cache_path())
try:
im = Image.open(self.image.path)
except IOError:
return
# Save the original format
im_format = im.format
# Apply effect if found
if self.effect is not None:
im = self.effect.pre_process(im)
elif photosize.effect is not None:
im = photosize.effect.pre_process(im)
# Resize/crop image
if im.size != photosize.size and photosize.size != (0, 0):
im = self.resize_image(im, photosize)
# Apply watermark if found
if photosize.watermark is not None:
im = photosize.watermark.post_process(im)
# Apply effect if found
if self.effect is not None:
im = self.effect.post_process(im)
elif photosize.effect is not None:
im = photosize.effect.post_process(im)
# Save file
im_filename = getattr(self, "get_%s_filename" % photosize.name)()
try:
if im_format != 'JPEG':
try:
im.save(im_filename)
return
except KeyError:
pass
im.save(im_filename, 'JPEG', quality=int(photosize.quality), optimize=True)
except IOError, e:
if os.path.isfile(im_filename):
os.unlink(im_filename)
raise e
def remove_size(self, photosize, remove_dirs=True):
if not self.size_exists(photosize):
return
filename = getattr(self, "get_%s_filename" % photosize.name)()
if os.path.isfile(filename):
os.remove(filename)
if remove_dirs:
self.remove_cache_dirs()
def clear_cache(self):
cache = PhotoSizeCache()
for photosize in cache.sizes.values():
self.remove_size(photosize, False)
self.remove_cache_dirs()
def pre_cache(self):
cache = PhotoSizeCache()
for photosize in cache.sizes.values():
if photosize.pre_cache:
self.create_size(photosize)
def remove_cache_dirs(self):
try:
os.removedirs(self.cache_path())
except:
pass
def save(self, *args, **kwargs):
if self.date_taken is None:
try:
exif_date = self.EXIF.get('EXIF DateTimeOriginal', None)
if exif_date is not None:
d, t = str.split(exif_date.values)
year, month, day = d.split(':')
hour, minute, second = t.split(':')
self.date_taken = datetime(int(year), int(month), int(day),
int(hour), int(minute), int(second))
except:
pass
if self.date_taken is None:
self.date_taken = datetime.now()
if self._get_pk_val():
self.clear_cache()
super(ImageModel, self).save(*args, **kwargs)
self.pre_cache()
def delete(self):
assert self._get_pk_val() is not None, "%s object can't be deleted because its %s attribute is set to None." % (self._meta.object_name, self._meta.pk.attname)
self.clear_cache()
super(ImageModel, self).delete()
class Photo(ImageModel):
title = models.CharField(_('title'), max_length=100, unique=True)
title_slug = models.SlugField(_('slug'), unique=True,
help_text=('A "slug" is a unique URL-friendly title for an object.'))
caption = models.TextField(_('caption'), blank=True)
date_added = models.DateTimeField(_('date added'), default=datetime.now, editable=False)
is_public = models.BooleanField(_('is public'), default=True, help_text=_('Public photographs will be displayed in the default views.'))
tags = TagField(help_text=tagfield_help_text, verbose_name=_('tags'))
class Meta:
ordering = ['-date_added']
get_latest_by = 'date_added'
verbose_name = _("photo")
verbose_name_plural = _("photos")
def __unicode__(self):
return self.title
def __str__(self):
return self.__unicode__()
def save(self, *args, **kwargs):
if self.title_slug is None:
self.title_slug = slugify(self.title)
super(Photo, self).save(*args, **kwargs)
def get_absolute_url(self):
return reverse('pl-photo', args=[self.title_slug])
def public_galleries(self):
"""Return the public galleries to which this photo belongs."""
return self.galleries.filter(is_public=True)
def get_previous_in_gallery(self, gallery):
try:
return self.get_previous_by_date_added(galleries__exact=gallery,
is_public=True)
except Photo.DoesNotExist:
return None
def get_next_in_gallery(self, gallery):
try:
return self.get_next_by_date_added(galleries__exact=gallery,
is_public=True)
except Photo.DoesNotExist:
return None
class BaseEffect(models.Model):
name = models.CharField(_('name'), max_length=30, unique=True)
description = models.TextField(_('description'), blank=True)
class Meta:
abstract = True
def sample_dir(self):
return os.path.join(settings.MEDIA_ROOT, PHOTOLOGUE_DIR, 'samples')
def sample_url(self):
return settings.MEDIA_URL + '/'.join([PHOTOLOGUE_DIR, 'samples', '%s %s.jpg' % (self.name.lower(), 'sample')])
def sample_filename(self):
return os.path.join(self.sample_dir(), '%s %s.jpg' % (self.name.lower(), 'sample'))
def create_sample(self):
if not os.path.isdir(self.sample_dir()):
os.makedirs(self.sample_dir())
try:
im = Image.open(SAMPLE_IMAGE_PATH)
except IOError:
raise IOError('Photologue was unable to open the sample image: %s.' % SAMPLE_IMAGE_PATH)
im = self.process(im)
im.save(self.sample_filename(), 'JPEG', quality=90, optimize=True)
def admin_sample(self):
return u'<img src="%s">' % self.sample_url()
admin_sample.short_description = 'Sample'
admin_sample.allow_tags = True
def pre_process(self, im):
return im
def post_process(self, im):
return im
def process(self, im):
im = self.pre_process(im)
im = self.post_process(im)
return im
def __unicode__(self):
return self.name
def __str__(self):
return self.__unicode__()
def save(self, *args, **kwargs):
try:
os.remove(self.sample_filename())
except:
pass
models.Model.save(self, *args, **kwargs)
self.create_sample()
for size in self.photo_sizes.all():
size.clear_cache()
# try to clear all related subclasses of ImageModel
for prop in [prop for prop in dir(self) if prop[-8:] == '_related']:
for obj in getattr(self, prop).all():
obj.clear_cache()
obj.pre_cache()
def delete(self):
try:
os.remove(self.sample_filename())
except:
pass
models.Model.delete(self)
class PhotoEffect(BaseEffect):
""" A pre-defined effect to apply to photos """
transpose_method = models.CharField(_('rotate or flip'), max_length=15, blank=True, choices=IMAGE_TRANSPOSE_CHOICES)
color = models.FloatField(_('color'), default=1.0, help_text=_("A factor of 0.0 gives a black and white image, a factor of 1.0 gives the original image."))
brightness = models.FloatField(_('brightness'), default=1.0, help_text=_("A factor of 0.0 gives a black image, a factor of 1.0 gives the original image."))
contrast = models.FloatField(_('contrast'), default=1.0, help_text=_("A factor of 0.0 gives a solid grey image, a factor of 1.0 gives the original image."))
sharpness = models.FloatField(_('sharpness'), default=1.0, help_text=_("A factor of 0.0 gives a blurred image, a factor of 1.0 gives the original image."))
filters = models.CharField(_('filters'), max_length=200, blank=True, help_text=_(IMAGE_FILTERS_HELP_TEXT))
reflection_size = models.FloatField(_('size'), default=0, help_text=_("The height of the reflection as a percentage of the orignal image. A factor of 0.0 adds no reflection, a factor of 1.0 adds a reflection equal to the height of the orignal image."))
reflection_strength = models.FloatField(_('strength'), default=0.6, help_text=_("The initial opacity of the reflection gradient."))
background_color = models.CharField(_('color'), max_length=7, default="#FFFFFF", help_text=_("The background color of the reflection gradient. Set this to match the background color of your page."))
class Meta:
verbose_name = _("photo effect")
verbose_name_plural = _("photo effects")
def pre_process(self, im):
if self.transpose_method != '':
method = getattr(Image, self.transpose_method)
im = im.transpose(method)
if im.mode != 'RGB' and im.mode != 'RGBA':
return im
for name in ['Color', 'Brightness', 'Contrast', 'Sharpness']:
factor = getattr(self, name.lower())
if factor != 1.0:
im = getattr(ImageEnhance, name)(im).enhance(factor)
for name in self.filters.split('->'):
image_filter = getattr(ImageFilter, name.upper(), None)
if image_filter is not None:
try:
im = im.filter(image_filter)
except ValueError:
pass
return im
def post_process(self, im):
if self.reflection_size != 0.0:
im = add_reflection(im, bgcolor=self.background_color, amount=self.reflection_size, opacity=self.reflection_strength)
return im
class Watermark(BaseEffect):
image = models.ImageField(_('image'), upload_to=PHOTOLOGUE_DIR+"/watermarks")
style = models.CharField(_('style'), max_length=5, choices=WATERMARK_STYLE_CHOICES, default='scale')
opacity = models.FloatField(_('opacity'), default=1, help_text=_("The opacity of the overlay."))
class Meta:
verbose_name = _('watermark')
verbose_name_plural = _('watermarks')
def post_process(self, im):
mark = Image.open(self.image.path)
return apply_watermark(im, mark, self.style, self.opacity)
class PhotoSize(models.Model):
name = models.CharField(_('name'), max_length=20, unique=True, help_text=_('Photo size name should contain only letters, numbers and underscores. Examples: "thumbnail", "display", "small", "main_page_widget".'))
width = models.PositiveIntegerField(_('width'), default=0, help_text=_('If width is set to "0" the image will be scaled to the supplied height.'))
height = models.PositiveIntegerField(_('height'), default=0, help_text=_('If height is set to "0" the image will be scaled to the supplied width'))
quality = models.PositiveIntegerField(_('quality'), choices=JPEG_QUALITY_CHOICES, default=70, help_text=_('JPEG image quality.'))
upscale = models.BooleanField(_('upscale images?'), default=False, help_text=_('If selected the image will be scaled up if necessary to fit the supplied dimensions. Cropped sizes will be upscaled regardless of this setting.'))
crop = models.BooleanField(_('crop to fit?'), default=False, help_text=_('If selected the image will be scaled and cropped to fit the supplied dimensions.'))
pre_cache = models.BooleanField(_('pre-cache?'), default=False, help_text=_('If selected this photo size will be pre-cached as photos are added.'))
increment_count = models.BooleanField(_('increment view count?'), default=False, help_text=_('If selected the image\'s "view_count" will be incremented when this photo size is displayed.'))
effect = models.ForeignKey('PhotoEffect', null=True, blank=True, related_name='photo_sizes', verbose_name=_('photo effect'))
watermark = models.ForeignKey('Watermark', null=True, blank=True, related_name='photo_sizes', verbose_name=_('watermark image'))
class Meta:
ordering = ['width', 'height']
verbose_name = _('photo size')
verbose_name_plural = _('photo sizes')
def __unicode__(self):
return self.name
def __str__(self):
return self.__unicode__()
def clear_cache(self):
for cls in ImageModel.__subclasses__():
for obj in cls.objects.all():
obj.remove_size(self)
if self.pre_cache:
obj.create_size(self)
PhotoSizeCache().reset()
def save(self, *args, **kwargs):
if self.crop is True:
if self.width == 0 or self.height == 0:
raise ValueError("PhotoSize width and/or height can not be zero if crop=True.")
super(PhotoSize, self).save(*args, **kwargs)
PhotoSizeCache().reset()
self.clear_cache()
def delete(self):
assert self._get_pk_val() is not None, "%s object can't be deleted because its %s attribute is set to None." % (self._meta.object_name, self._meta.pk.attname)
self.clear_cache()
super(PhotoSize, self).delete()
def _get_size(self):
return (self.width, self.height)
def _set_size(self, value):
self.width, self.height = value
size = property(_get_size, _set_size)
class PhotoSizeCache(object):
__state = {"sizes": {}}
def __init__(self):
self.__dict__ = self.__state
if not len(self.sizes):
sizes = PhotoSize.objects.all()
for size in sizes:
self.sizes[size.name] = size
def reset(self):
self.sizes = {}
# Set up the accessor methods
def add_methods(sender, instance, signal, *args, **kwargs):
""" Adds methods to access sized images (urls, paths)
after the Photo model's __init__ function completes,
this method calls "add_accessor_methods" on each instance.
"""
if hasattr(instance, 'add_accessor_methods'):
instance.add_accessor_methods()
# connect the add_accessor_methods function to the post_init signal
post_init.connect(add_methods)