It's much easier to explain my doubts with an example:

I have a list with dictionaries of this type,

[
    {
     'portal_id': 5, 
     'url_imovel': 'asd.pt', 
     'url_photos': {0: 'pfoto1.pt', 1: 'pphoto2.pt'}, 
     'total_photos': 2
    }, 
    {
     'portal_id': 5, 
     'url_imovel': 'asd2.pt', 
     'url_photos': {0: 'pfoto12.pt', 1: 'pphoto22.pt'}, 
     'total_photos': 2
    },
    {
     'portal_id': 5, 
     'url_imovel': 'foo.pt', 
     'url_photos': {0: 'fotofoo1.pt', 1: 'photofoo2.pt', 1: 'photofoo3.pt'}, 
     'total_photos': 3
    }
]

The dictionary is generated as follows:

all_im_fotos = []

    im_fotos = {
        "portal_id" : 5,
        "url_imovel" : str(),
        "url_photos" : dict(),
        "total_photos": int()
    }

    urls = "asd.pt"
    photos_url = ["pfoto1.pt", "pphoto2.pt"]

    im_fotos["url_imovel"] = urls
    for i in range(len(photos_url)):
        im_fotos["url_photos"].update({i: photos_url[i]})
    im_fotos["total_photos"] = len(im_fotos["url_photos"])

    all_im_fotos.append(im_fotos)

    ... same process ...

My question is, how can I compare the insertion of new values. My goal is to create a new dictionary that just insert new values, increasing the index of imfotos. For example:

difference = []
new_imovel = "asd.pt"
new_url_photos = ["pfoto1.pt", "pfoto3.pt"]

There is a new photo for the url "asd.pt", so we should add the difference by auto incrementing the index, resulting in:

[
        {
         'portal_id': 5, 
         'url_imovel': 'asd.pt', 
         'url_photos': {0: 'pfoto1.pt', 1: 'pphoto2.pt', 2: 'pfoto3.pt'}, 
         'total_photos': 3
        }
]

How can I make this as simple as possible? is it possible to save this dictionary as a json file in order to perform the same process later?