Search for many rows with many distinct values

I am looking to implement a cache in MySQL. I'm doing this because the app I'm developing needs a cache but has no persistence.

I am keeping a collection of SHA-1 checksums for files. The user can provide me with a list of checksums, and I need to return to them which checksums I do not have in my database. I'm expecting the number of checksums in my database to be on the order of a million, and the number of values to check to be on the order of a hundred thousand.

The naive approach would be to issue a long string of

SELECT COUNT(*) FROM myTable WHERE checksum = '2fd4e1c67a2d28fced849ee1bb76e7391b93eb12';

This could be optimized somewhat by using the ability to use parameters with the Python connector. However, this seems like a lot of churn across the connection between the python process and the MySQL process.

I know there is an approach along the lines of SELECT checksum FROM myTable NOT IN (SELECT someOtherTable WHERE someClause), which is a match for what I need except that the list of checksums to check against is in my Python process, not a MySQL table.

What is the best way to find checksums that are not in a list which is initially only available in my Python process (so this must be shared across to MySQL across IPC)?