Am trying to create a thumbnail in django, am trying to build a custom class specifically to be used for generating thumbnails. As following

from StringIO import StringIO
from PIL import Image

class Thumbnail(object):
    source  = ''
    size    = (50, 50)
    output = ''

    def __init__(self):
        pass

    @staticmethod
    def load(src):
        self        = Thumbnail()
        self.source = src

        return self

    def generate(self, size=(50, 50)):
        if not isinstance(size, tuple):
            raise Exception('Thumbnail class: The size parameter must be an instance of a tuple.')

        self.size   = size
        # resize properties
        box = self.size
        factor = 1
        fit = True
        image = Image.open(self.source)
        # Convert to RGB if necessary
        if image.mode not in ('L', 'RGB'): image = image.convert('RGB')
        while image.size[0]/factor > 2*box[0] and image.size[1]*2/factor > 2*box[1]:
            factor *=2
        if factor > 1:
            image.thumbnail((image.size[0]/factor, image.size[1]/factor), Image.NEAREST)

        #calculate the cropping box and get the cropped part
        if fit:
            x1 = y1 = 0
            x2, y2 = image.size
            wRatio = 1.0 * x2/box[0]
            hRatio = 1.0 * y2/box[1]
            if hRatio > wRatio:
                y1 = int(y2/2-box[1]*wRatio/2)
                y2 = int(y2/2+box[1]*wRatio/2)
            else:
                x1 = int(x2/2-box[0]*hRatio/2)
                x2 = int(x2/2+box[0]*hRatio/2)
            image = image.crop((x1,y1,x2,y2))

        #Resize the image with best quality algorithm ANTI-ALIAS
        image.thumbnail(box, Image.ANTIALIAS)

        # save image to memory
        temp_handle = StringIO()
        image.save(temp_handle, 'png')
        temp_handle.seek(0)

        self.output = temp_handle

        return self

    def get_output(self):
        return self.output.read()

the purpose of the class is so i can use it inside different locations to generate thumbnails on the fly. The class works perfectly, I've tested it directly under a view.. I've implemented the thumbnail class inside the save method of the forms to resize the original images on saving.

in my design, I have two fields for thumbnails. I was able to generate one thumbnail, if I try to generate two it crashes and I've been stuck for hours not sure whats the problem.

Here is my model

class Image(models.Model):
    article         = models.ForeignKey(Article)
    title           = models.CharField(max_length=100, null=True, blank=True)
    src             = models.ImageField(upload_to='publication/image/')
    r128            = models.ImageField(upload_to='publication/image/128/', blank=True, null=True)
    r200            = models.ImageField(upload_to='publication/image/200/', blank=True, null=True)

    uploaded_at     = models.DateTimeField(auto_now=True)

Here is my forms

class ImageForm(models.ModelForm):
    """

    """
    class Meta:
        model = Image
        fields = ('src',)


    def save(self, commit=True):
        instance = super(ImageForm, self).save(commit=True)

        file = Thumbnail.load(instance.src)

        instance.r128 = SimpleUploadedFile(
                    instance.src.name,
                    file.generate((128, 128)).get_output(),
                    content_type='image/png'
                )


        instance.r200 = SimpleUploadedFile(
            instance.src.name,
            file.generate((200, 200)).get_output(),
            content_type='image/png'
        )

        if commit:
            instance.save()
        return instance

the strange part is, when i remove the line which contains instance.r200 in the form save. It works fine, and it does the thumbnail and stores it successfully. Once I add the second thumbnail it fails..

Any ideas what am doing wrong here?

Thanks

Update:

I tried earlier doing the following but I still got the same error

class ImageForm(models.ModelForm):
    """

    """
    class Meta:
        model = Image
        fields = ('src',)


    def save(self, commit=True):
        instance = super(ImageForm, self).save(commit=True)


        instance.r128 = SimpleUploadedFile(
                    instance.src.name,
                    Thumbnail.load(instance.src).generate((128, 128)).get_output(),
                    content_type='image/png'
                )


        instance.r200 = SimpleUploadedFile(
            instance.src.name,
            Thumbnail.load(instance.src).generate((200, 200)).get_output(),
            content_type='image/png'
        )

        if commit:
            instance.save()
        return instance