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我定义了一个函数 _set_thumbnail 将属性附加到对象。

   class StdImageField(ImageField):
    def __init__(self, verbose_name=None, name=None, width_field=None,
        height_field=None, sizes=None, **kwargs):

        self.sizes = sizes
        super(StdImageField, self).__init__(verbose_name, name, width_field,
            height_field, **kwargs)

    def contribute_to_class(self, cls, name):
        """Call methods for generating all operations on specified signals"""
        super(StdImageField, self).contribute_to_class(cls, name)
        signals.post_save.connect(self.resize_image, sender=cls)
        signals.post_init.connect(self._set_thumbnail, sender=cls)

    def resize_image(self, instance=None, **kwargs):
        if getattr(instance, self.name):
            filename = getattr(instance, self.name).path
            shutil.copyfile(filename, '%s/%d-0.jpg' % (os.path.dirname(filename), instance._get_pk_val()))
            for i, size in enumerate(self.sizes):
                img = Image.open(filename)
                img = ImageOps.fit(img, size, method=Image.ANTIALIAS)
                new_filename = '%s/%d-%d.jpg' % (os.path.dirname(filename), instance._get_pk_val(), i + 1)
                img.save(new_filename, "JPEG", quality=100)

    def _set_thumbnail(self, instance=None, **kwargs):
        if getattr(instance, self.name):
            for i, size in enumerate(self.sizes):
                setattr(getattr(instance, self.name), 'image%d' % (i + 1), '%s%d-%d.jpg' % ('s/', instance._get_pk_val(), i + 1))

它可以通过 Django admin 完美运行。但是，在通过前端使用它时出现错误：

TypeError（ %d 格式：需要一个数字，而不是 NoneType ）

任何建议将不胜感激。谢谢。

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