Question

So I have a form in Django that is used to upload an image to an ImageField. This works well. I then pass off the request.FILES[‘image’] off to a function called MakeThumbnail for further processing.

MakeThumbnail is not working too well. I have assembled this from a series of StackOverflow threads, but I think I am missing some crucial concepts. Here is my code.

    def MakeThumbnail(file):
        img = Image.open(file)
        thumbnail = img.thumbnail((128, 128), Image.ANTIALIAS)
        thumbnailString = StringIO.StringIO(thumbnail)
        newFile = ContentFile(thumbnailString)
        return newFile

The stacktrace says I am failing on this line: newFile = ContentFile(thumbnailString). It gives me the following error: expected read buffer, instance found

I think I might be failing back at thumbnail = img.thumbnail((128, 128), Image.ANTIALIAS), though, after looking at the local variables:

thumbnailString : <StringIO.StringIO instance at 0x0000000003B39748>
file : <InMemoryUploadedFile: Desert.jpg (image/jpeg)>
thumbnail : None
img : <PIL.JpegImagePlugin.JpegImageFile image mode=RGB size=128x96 at 0x3B25C08>

Notice that thumbnail is none. It should contain something. Does anyone have some hints for me?

thank you!

Answer 1

Thank you so much for the help, Jan Spurny. I figured it out with your help. So, when img is saved to thumbnailString, a few things need to happen. The code above actually produces an error because we pass an instance to ContentFile instead of a buffer. No matter, we just need to call thumbnailString.read(). But thumbnailString.read() returns ”. Turns out we need to do thumbnailString.seek(0) beforehand. But this did not work either!

Ultimately, I was able to get the image file back to a Django file using InMemoryUploadedFile.

Here is what the code looks like, from beginning to end:

from django.core.files.uploadedfile import InMemoryUploadedFile
import StringIO
def MakeThumbnail(file):
    img = Image.open(file)
    img.thumbnail((128, 128), Image.ANTIALIAS)
    thumbnailString = StringIO.StringIO()
    img.save(thumbnailString, 'JPEG')
    newFile = InMemoryUploadedFile(thumbnailString, None, 'temp.jpg', 'image/jpeg', thumbnailString.len, None)
    return newFile