Python/Django - Value is reverting back after for loop

Question

I'm trying to pass the URL's of a list of photos to the template. I'm concatenating my MEDIA_URL to every photo name.

When print(a) is run, I can see in the console that the concatenation was successfully added. The result is something like media/photo.jpg. However by the time the loop finishes, the result reverts back to the original photo.jpg as if no concatenation happened. print(photos) shows a list of photos with no changes.

Why?

def get_property_data(request):
    property_id = request.GET.get('id')
    photos = ListingPhoto.objects.values_list('photo', flat=True).filter(listing__id=property_id)
    for a in photos:
        a = settings.MEDIA_URL + a
        print(a)
    print(photos)

    return JsonResponse({'property': list(photos)})

In for a in photos, a is copy of the elements inside photos. Therefore modifying a doesn't modify the values in the iterable photos. Maybe you want: for i in range(len(photos)): photos[i] += settings.MEDIA_URL. — Abdou
– Abdou, Commented Dec 23, 2017 at 3:29

WombatPM · Accepted Answer · 2017-12-23 03:29:38Z

1

You are outputting photos which is unchanged. Also you are looping through on a and changing the value, over and over again.

Try something like this instead

b = []
for a in photos:
        b.append(settings.MEDIA_URL + a)
        print(a)
print(b) # b is an array of url strings

answered Dec 23, 2017 at 3:29

WombatPM

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