I am trying to update/append a list of dictionary items based on another list.

**ParentList**

```
{'date': '2019-03-07', 'start_time': '2019-03-07 10:08:21', 'duration': '5'}     
{'date': '2019-03-07', 'start_time': '2019-03-07 10:14:43', 'duration': '15'}
{'date': '2019-03-07', 'start_time': '2019-03-07 10:31:22', 'duration': '13'}

```

**NewList**

```
{'date': '2019-03-07', 'start_time': '2019-03-07 10:08:21', 'duration': '5'}     
{'date': '2019-03-07', 'start_time': '2019-03-07 10:14:43', 'duration': '15'}
{'date': '2019-03-09', 'start_time': '2019-03-09 10:31:22', 'duration': '13'}
{'date': '2019-03-10', 'start_time': '2019-03-10 10:31:22', 'duration': '13'}
{'date': '2019-03-11', 'start_time': '2019-03-11 10:31:22', 'duration': '13'}
{'date': '2019-03-12', 'start_time': '2019-03-12 10:31:22', 'duration': '13'}

```

I want to update the **ParentList** with the new items in the **NewList**. As you can see, the first 2 items from the latter are repeated in the former. So I want to add only the last 4 items(from **NewList**) into the **ParentList**.

The simple method would be to iterate through each **NewList** item and check if it already exists in the **ParentList**.

**Code** 

```
for newItem in NewList:
    bln_item_exists = False
    for parentItem in ParentList:
        if dict(newItem).get("date") == dict(parentItem).get("date") and dict(newItem).get("start_time") == dict(parentItem).get("start_time"):
            bln_item_exists = True
            break
    if not bln_item_exists:
        items_to_append.append(newItem)

```

I am worried that as my DB size increases, the performance would be hit, is there a more efficient way to do the same ?