Unfortunately, the sqlite3 python interface doesn't expose Sqlite's extended error info so that you could see what's happening.

https://bugs.python.org/issue16379

There an uncommitted patch to get the extended error in this other, related issue: https://bugs.python.org/issue24139

Or maybe just try cffi or ctypes in python to call sqlite3_errcode(), sqlite3_extended_errcode() and sqlite3_errmsg(). The incantation to find an already linked sqlite3 lib:

import ctypes

import ctypes.util

sqlite = ctypes.CDLL(ctypes.util.find_library('sqlite3'))