SQLAlchemy: Insert or Update when column value is a duplicate

Question

I have a table A with the following columns:

• id UUID
• str_identifier TEXT
• num FLOAT

and a table B with similar columns:

• str_identifier TEXT
• num FLOAT
• entry_date TIMESTAMP

I want to construct a sqlalchemy query that does the following:

• finds entries in table B that either do not exist yet in table A, and inserts them
• finds entries in table B that do exist in table A but have a different value for the num column

The catch is that table B has the entry_date column, and as a result can have multiple entries with the same str_identifier but different entry dates. So I always want to perform this insert/update query using the latest entry for a given str_identifier (if it has multiple entries in table B).

For example, if before the query runs tables A and B are:

[A]
|  id | str_identifier  |  num  |
|-----|-----------------|-------|
| 1   | str_id_1        |   25  |


[B]
| str_identifier | num | entry_date |
|----------------|-----|------------|
| str_id_1       | 89  | 2020-07-20 |
| str_id_1       | 25  | 2020-06-20 |
| str_id_1       | 50  | 2020-05-20 |
| str_id_2       | 45  | 2020-05-20 |

After the update query, table A should look like:

[A]
|  id | str_identifier  | num |
|-----|-----------------|-----|
|  1  | str_id_1        | 89  |
|  2  | str_id_2        | 45  |

The query I've constructed so far should detect difference, but will adding order_by(B.entry_date.desc()) ensure I only do the exist comparisons with the latest str_identifier values?

My Current Query

query = (
        select([B.str_identifier, B.value])
        .select_from(
            join(B, A, onclause=B.str_identifier == A.str_identifier, isouter=True)
        )
        .where(
            and_(
                ~exists().where(
                    and_(
                        B.str_identifier == A.str_identifier,
                        B.value == A.value,
                        ~B.value.in_([None]),
                    )
                )
            )
        )
    )