The standard example for writing data with mutations uses database.batch: https://cloud.google.com/spanner/docs/getting-started/python#write-data-with-mutations

database.batch however does not automatically retry the transaction if it is aborted by Spanner. This causes errors if you try to use this method to insert a large amount of data, or if there are lock contentions on the data that you insert.

Either:

1. The sample(s) should be updated to show how to use run_in_transaction to use mutations.
2. And/or: database.batch should also automatically retry aborted transactions.