Вадим Шаталов

In [1]: from collections import defaultdict

In [2]: dict1 = {"a1": "a2", "a2": "a3", "a3": "a5"}
   ...: dict2 = {"a1": "a4", "a2": "a5"}

In [3]: dd = defaultdict(list)

In [4]: for key in set(list(dict1.keys())+list(dict2.keys())):
   ...:     if key in dict1:
   ...:         dd[key].append(dict1[key])
   ...:     if key in dict2:
   ...:         dd[key].append(dict2[key])
   ...:

In [5]: dd
Out[5]: defaultdict(list, {'a2': ['a3', 'a5'], 'a1': ['a2', 'a4'], 'a3': ['a5']})

from django.http import JsonResponse
def search_photos(request):
    if request.method == 'GET':
        q = request.GET.get('q')
        photos_url = []
        #Здесь формирую массив photos_url
        return JsonResponse(photos_url)

def proccess(line):
    while True:
        try:
            # do something
            return result
        except:
            # do something
            if max_retries: # условие выхода
                return error

for string in file:
    result = proccess(string)
    ...