How to update list contents

September 19, 2023

I have two list

A = [
    {'name':'Tom', 'country':'American', 'birthday': '2001'},
    {'name':'Tim', 'country':'India'},
    {'name':'Peter', 'country':'China'},
]
B = [
    {'name':'Tom', 'country':'China', 'birthday': '...', 'dream': '...'},
]

We think the list A was a new list and the list B was the old list.I have some problem about how to write a code to upgrade the old list.
The result will be：

[{'name': 'Tom', 'country': 'China', 'birthday': '2001', 'dream': '...'},
 {'name': 'Tim', 'country': 'India'},
 {'name': 'Peter', 'country': 'China'}]

I don’t have any idea about this.

>Solution :

Assuming you want to update all keys, using "name" as merging key.

You can build a dictionary of B using the name as key, then loop over A to update each dictionary:

B_dict = {d['name']: d for d in B if 'name' in d}

for d in A:
    if 'name' in d:
        d.update(B_dict.get(d['name'], {}))

Output:

[{'name': 'Tom', 'country': 'China', 'birthday': '...', 'dream': '...'},
 {'name': 'Tim', 'country': 'India'},
 {'name': 'Peter', 'country': 'China'}]

Just in case ... have a special meaning and you only want to add them if there is not already a non ... value, you can tweak the above approach to only pass the key:... for which there is not already an existing valid value:

B_dict = {d['name']: d for d in B if 'name' in d}
for d in A:
    if 'name' in d:
        d.update({k: v for k,v in B_dict.get(d['name'], {}).items()
                  if v != '...' or k not in d})

Output:

[{'name': 'Tom', 'country': 'China', 'birthday': '2001', 'dream': '...'},
 {'name': 'Tim', 'country': 'India'},
 {'name': 'Peter', 'country': 'China'}]