Django - for-loop with variable field name

Question

Recently I started experimenting with Python and Django. I like it, learned already a lot, but still a long way to go...

I made a model containing 5 image fields. Next to the model I also made a form to enter data and save it. So far so good. Now I want to write another form to 'edit' the uploaded images, meaning:

upload new images
delete the 'old' images from the database

I wrote the code below that does the job for 1 image:

if form.is_valid():
            form_image = form.cleaned_data['image_1']
            try:
                details = Model.objects.get(pk=pk)
                if details.image_1 != form_image:
                    details.image_1.delete(save=False)
            except: pass # when new photo then we do nothing, normal case
            form.save()

But I am struggling with following problems:

How can this code be rewritten to update 5 image fields? Because in worst case one can edit all 5 image fields. I tried with a 'for loop' but never succeed. For example:

image_list = [image_1, image_2, image_3, image_4, image_5]
if form.is_valid():
    for image in image_list:
        form_image = form.cleaned_data[image]
        try:
            details = Model.objects.get(pk=pk)
            if details.image != form_image:
                details.image.delete(save=False)
        except: pass # when new photo then we do nothing, normal case
        form.save()

Are there more intelligent ways to write this piece of logic. A problem that I have with this code is that it checks on the name of the image. And probably this goes wrong when I have multiple images with the same name...

Hopefully someone can give some feedback and point me again in the right direction.

Many thanks!

Kind Regards

Hi again, the naming issue is solved: I can make the image name unique, using this renaming technique: [Django FileField with upload_to determined at runtime](http://stackoverflow.com/questions/1190697/django-filefield-with-upload-to-determined-at-runtime). But still the first point remains: how to loop over different images? And is this piece of code 'intelligent' meaning, is this the best way to handle the image upload? Thanks! — Köver, Jun 19 '12 at 16:13

jdi · Accepted Answer · 2012-06-20T19:31:37.463

You need to use strings:

image_list = ['image_1', 'image_2', 'image_3', 'image_4', 'image_5']

# or doing that dynamically as well:
image_list = ['image_%d' % i for i in xrange(1,6)]

Also, from your example, I am not sure where you are getting a unique pk value each time. But assume each loop should produce a different details object to compare to that specific image.

One thing to consider is that you should almost never do a blanket try, except: pass. It can easily mask errors that you didn't consider:

try:
    details = Model.objects.get(pk=pk)
    ...
# django models have a special exception type
# when they don't exist.
except Model.DoesNotExist: 
    pass

In order to dynamically use those string names as variable lookups, you just need to use getattr

for image_name in image_list:
    ...
    # equiv to: details.image_1, details.image_2, ...
    if getattr(details, image_name, None) != form_image:
    ...

Thanks for the feedback jdi. The problem with the strings is that I can't use it for the `details.image`. In the code I actually want to loop with the same variable on two places: `form.cleaned_data['variable']` and `details.variable`. Is this possible somehow? Thanks! — Köver, Jun 20 '12 at 19:15

Django - for-loop with variable field name

1 Answers1