Ivan

with open(path_in, 'w+') as read_file:
    read_file.write('something')

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
           'builtins': 'app.templatetags.extratags' # <<<<<<<<<<<<<<<
        },
    },
]

def get_lenta_elem(request):
    items = Product.objects.all()
    return  {'items': items }

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
                # custom context processor
                'путь_к_файлу.навание_метода' # <<<<<<<<<<<<<
            ],
        },
    },
]

<input type="radio" name="choice" value="choice1">
<input type="radio" name="choice" value="choice2">
<input type="radio" name="choice" value="choice3">

choice = request.POST['choice']
print(choice)
>>> choice1

choice = request.POST.get('choice', None)
if choice:
    делать ваш код
else:
    вы не выбрали батон

class SupplyAdmin(admin.ModelAdmin):
   available_fields = ('name', 'field1', 'field2')
   hidden_fields = ('field3',)
   def get_form(self, request, obj, **kwargs):                             
       if request.user.username == 'example@example.com':                                            
           self.fields = self.available_fields + self.hidden_fields         
       else:                                                                    
           self.fields = self.available_fields

        return super(SupplyAdmin, self).get_form(request, obj, **kwargs)

class ItemAttributeValue(models.Model):
    att1 = .....
    att2 = .....
    item = models.ForeignKey(ItemAttribute, related_name='attribute')

characteristics = ItemAttribute.objects.get(category=3)

{% for i in characteristics %}
{{ i.name}}
...
{{ i.attribute.att1}}
...
{% endfor %}