sqlite3 foreign key

[Larz60+]

First, because you use the python wrapper to sqlite3, the DBMS does not automatically become part of python, it's still sqlite3,
not Python.
I'd use the sqlite3 interface to open the database and check the schema of the tables in question to make sure the constraints are there.
From command line (in database directory), type slqite3 databasename
at the prompt 'sqlite>' type .schema
check the tables to make sure constraint exists.
Then try to manually insert commands.
.quit to exit