将图像分配给ImageField而不保存（Django）

Question

我的代码：

class AttackImage(models.Model):
    title = models.CharField(max_length=255)
    image = models.ImageField(upload_to='attack_images', blank=True, null=True)
    source_url = models.URLField(blank=True,null=True)
    domain = models.ForeignKey(Domain, on_delete=models.CASCADE, blank=True, null=True)
    creator = models.ForeignKey(User, on_delete=models.CASCADE, blank=True,null=True)
    slug = models.SlugField(blank=True,null=True)

    def save(self, *args, **kwargs):
        if not self.slug:
            self.slug = slugify(self.title)[:50]

        if self.source_url and not self.image:
            result = urllib.request.urlretrieve(self.source_url)
            self.image = os.path.basename(self.source_url), File(open(result[0], 'rb'))

        if self.source_url:
            if '//' in self.source_url:
                d = self.source_url.split('//')[1].split('/')[0]
            else:
                d = self.source_url.split('/')[0]

            try:
                domain = Domain.objects.get(domain_url=d)
            except Exception as e:
                print(e)
                domain_object = Domain.objects.create(domain_url=d)
                domain = domain_object
            self.domain = domain

        return super(AttackImage, self).save(*args, **kwargs)

错误：

Traceback (most recent call last):
  File "crawl_ebaumsworld.py", line 92, in <module>
    crawl(first_url)
  File "crawl_ebaumsworld.py", line 66, in crawl
    creator=mike
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/query.py", line 422, in create
    obj.save(force_insert=True, using=self.db)
  File "/home/michael/projects/deepsteg/engine/models.py", line 62, in save
    return super(AttackImage, self).save(*args, **kwargs)
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/base.py", line 741, in save
    force_update=force_update, update_fields=update_fields)
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/base.py", line 779, in save_base
    force_update, using, update_fields,
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/base.py", line 870, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/base.py", line 908, in _do_insert
    using=using, raw=raw)
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/query.py", line 1186, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1334, in execute_sql
    for sql, params in self.as_sql():
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1278, in as_sql
    for obj in self.query.objs
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1278, in <listcomp>
    for obj in self.query.objs
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1277, in <listcomp>
    [self.prepare_value(field, self.pre_save_val(field, obj)) for field in fields]
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1228, in pre_save_val
    return field.pre_save(obj, add=True)
  File "/home/michael/projects/deepsteg/venvdeepsteg/lib/python3.6/site-packages/django/db/models/fields/files.py", line 286, in pre_save
    if file and not file._committed:
AttributeError: 'tuple' object has no attribute '_committed'

在crawl_ebaumsworld.py中，我创建了AttackImage对象：

attack_image_object = AttackImage.objects.create(
                    title=img_filename,
                    source_url=im_url,
                    creator=mike
                )

请参阅models.py中的AttackImage代码。我不能做self.image.save（）（没有错误），因为调用了super。我的问题是，不使用.save（）将图像分配给ImageField的正确方法是什么？预先感谢您的帮助。