如何在内存中创建一个文件(不是上传的文件)并通过django默认存储保存到filefield?

如果我要在内存中创建一个类似csv的文件对象,如下所示:

output_stream = io.StringIO()
sheet = pyexcel.get_sheet(records=data)
sheet.save_to_memory(file_type='csv', stream=output_stream)

如何将输出流中类似文件的对象保存到Django默认存储后端的文件中?

class Example(models.Model):
    model_file = models.FileField(upload_to='', max_length=255, blank=True, null=True)

我试过这样的方法:

self.model_file.save(filename, ContentFile(output_stream.read()))

但我得到了以下错误:

"TypeError: ('data must be bytes, received', <class 'str'>)"

PyExcel仅支持CSV类型文件的IO.StringIO流。

回溯:

...
  File "C:\Users\Cole\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\core\files\storage.py", line 49, in save
    return self._save(name, content)
  File "C:\Users\Cole\AppData\Local\Programs\Python\Python36-32\lib\site-packages\storages\backends\gcloud.py", line 167, in _save
    content_type=file.mime_type)
  File "C:\Users\Cole\AppData\Local\Programs\Python\Python36-32\lib\site-packages\google\cloud\storage\blob.py", line 1034, in upload_from_file
    size, num_retries, predefined_acl)
  File "C:\Users\Cole\AppData\Local\Programs\Python\Python36-32\lib\site-packages\google\cloud\storage\blob.py", line 947, in _do_upload
    size, num_retries, predefined_acl)
  File "C:\Users\Cole\AppData\Local\Programs\Python\Python36-32\lib\site-packages\google\cloud\storage\blob.py", line 759, in _do_multipart_upload
    transport, data, object_metadata, content_type)
  File "C:\Users\Cole\AppData\Local\Programs\Python\Python36-32\lib\site-packages\google\resumable_media\requests\upload.py", line 94, in transmit
    data, metadata, content_type)
  File "C:\Users\Cole\AppData\Local\Programs\Python\Python36-32\lib\site-packages\google\resumable_media\_upload.py", line 270, in _prepare_request
    raise TypeError(u'`data` must be bytes, received', type(data))
TypeError: ('`data` must be bytes, received', <class 'str'>)