Exceptions and Errors
exceptions to indicate an error has
happened. The SQLite library uses integer error codes. APSW maps between the two
systems as needed. Exceptions raised in Python code called by SQLite
will have that exception present when control returns to Python, and
SQLite will understand that an error occurred.
There are a few places where it is not possible for a Python exception to be reported to SQLite as an error, typically because SQLite does not allow an error to be signalled in that context. Another example would be in VFS code, because SQLite takes actions to recover from errors (eg it may try to rollback a transaction on a write error). Python wants to return to callers, not continue execution while the exception is pending. (Also only one exception can be active at a time.)
Unraisable exceptions in VFS code are handled by calling
VFSFile.excepthook() (more info). In other code sys.unraisablehook is
called, and if that is not present then sys.excepthook is
sqlite3_log is also called so that you will have the context of when the exception happened relative to the errors SQLite is logging.
- exception Error
This is the base for APSW exceptions.
For exceptions corresponding to SQLite error codes codes this attribute is the numeric error code.
APSW runs with extended result codes turned on. This attribute includes the detailed code.
As an example, if SQLite issued a read request and the system returned less data than expected then
resultwould have the value SQLITE_IOERR while
extendedresultwould have the value SQLITE_IOERR_SHORT_READ.
The location of the error in the SQL when encoded in UTF-8. The value is from sqlite3_error_offset, and will be -1 when a specific token in the input is not the cause.
APSW specific exceptions
The following exceptions happen when APSW detects various problems.
- exception ThreadingViolationError
You have used an object concurrently in two threads. For example you may try to use the same cursor in two different threads at the same time, or tried to close the same connection in two threads at the same time.
You can also get this exception by using a cursor as an argument to itself (eg as the input data for
Cursor.executemany()). Cursors can only be used for one thing at a time.
- exception ForkingViolationError
- exception IncompleteExecutionError
You have tried to start a new SQL execute call before executing all the previous ones. See the execution model for more details.
- exception ConnectionNotClosedError
This exception is no longer generated. It was required in earlier releases due to constraints in threading usage with SQLite.
- exception ConnectionClosedError
You have called
Connection.close()and then continued to use the
- exception CursorClosedError
You have called
Cursor.close()and then tried to use the cursor.
- exception BindingsError
There are several causes for this exception. When using tuples, an incorrect number of bindings where supplied:
cursor.execute("select ?,?,?", (1,2)) # too few bindings cursor.execute("select ?,?,?", (1,2,3,4)) # too many bindings
You are using named bindings, but not all bindings are named. You should either use entirely the named style or entirely numeric (unnamed) style:
cursor.execute("select * from foo where x=:name and y=?")
- exception ExecutionCompleteError
A statement is complete but you try to run it more anyway!
- exception ExecTraceAbort
The execution tracer returned False so execution was aborted.
- exception VFSNotImplementedError
A call cannot be made to an inherited Virtual File System (VFS) method as the VFS does not implement the method.
- exception VFSFileClosedError
The VFS file is closed so the operation cannot be performed.
The following lists which Exception classes correspond to which SQLite error codes.
- exception SQLError
SQLITE_ERROR. This error is documented as a bad SQL query or missing database, but is also returned for a lot of other situations. It is the default error code unless there is a more specific one.
- exception MismatchError
SQLITE_MISMATCH. Data type mismatch. For example a rowid or integer primary key must be an integer.
- exception NotFoundError
SQLITE_NOTFOUND. Returned when various internal items were not found such as requests for non-existent system calls or file controls.
- exception InternalError
SQLITE_INTERNAL. (No longer used) Internal logic error in SQLite.
- exception ProtocolError
SQLITE_PROTOCOL. (No longer used) Database lock protocol error.
- exception MisuseError
SQLITE_MISUSE. SQLite library used incorrectly - typically similar to ValueError in Python. Examples include not having enough flags when opening a connection (eg not including a READ or WRITE flag), or out of spec such as registering a function with more than 127 parameters.
- exception RangeError
SQLITE_RANGE. (Cannot be generated using APSW). 2nd parameter to sqlite3_bind out of range
- exception PermissionsError
SQLITE_PERM. Access permission denied by the operating system, or parts of the database are readonly such as a cursor.
- exception ReadOnlyError
SQLITE_READONLY. Attempt to write to a readonly database.
- exception CantOpenError
SQLITE_CANTOPEN. Unable to open the database file.
- exception AuthError
- exception AbortError
SQLITE_ABORT. Callback routine requested an abort.
- exception BusyError
SQLITE_BUSY. The database file is locked. Use
Connection.setbusytimeout()to change how long SQLite waits for the database to be unlocked or
Connection.setbusyhandler()to use your own handler.
- exception LockedError
SQLITE_LOCKED. A table in the database is locked.
- exception InterruptError
SQLITE_INTERRUPT. Operation terminated by sqlite3_interrupt - use
- exception SchemaChangeError
SQLITE_SCHEMA. The database schema changed. A
prepared statementbecomes invalid if the database schema was changed. Behind the scenes SQLite reprepares the statement. Another or the same
Connectionmay change the schema again before the statement runs. SQLite will attempt up to 5 times before giving up and returning this error.
- exception ConstraintError
SQLITE_CONSTRAINT. Abort due to constraint violation. This would happen if the schema required a column to be within a specific range.
- exception NoMemError
SQLITE_NOMEM. A memory allocation failed.
- exception IOError
SQLITE_IOERR. Some kind of disk I/O error occurred. The extended error code will give more detail.
- exception CorruptError
SQLITE_CORRUPT. The database disk image appears to be a SQLite database but the values inside are inconsistent.
- exception FullError
SQLITE_FULL. The disk appears to be full.
- exception TooBigError
SQLITE_TOOBIG. String or BLOB exceeds size limit. You can change the limits using
- exception NoLFSError
SQLITE_NOLFS. SQLite has attempted to use a feature not supported by the operating system such as large file support.
- exception EmptyError
SQLITE_EMPTY. Database is completely empty.
- exception FormatError
SQLITE_FORMAT. (No longer used) Auxiliary database format error.
- exception NotADBError
SQLITE_NOTADB. File opened that is not a database file. SQLite has a header on database files to verify they are indeed SQLite databases.
Augmented stack traces
When an exception occurs, Python does not include frames from non-Python code (ie the C code called from Python). This can make it more difficult to work out what was going on when an exception occurred for example when there are callbacks to collations, functions or virtual tables, triggers firing etc.
This is an example showing the difference between the tracebacks you would have got with earlier versions of apsw and the augmented traceback:
import apsw def myfunc(x): 1/0 con=apsw.Connection(":memory:") con.createscalarfunction("foo", myfunc) con.createscalarfunction("fam", myfunc) cursor=con.cursor() cursor.execute("create table bar(x,y,z);insert into bar values(1,2,3)") cursor.execute("select foo(1) from bar")
Traceback (most recent call last): File "t.py", line 11, in <module> cursor.execute("select foo(1) from bar") File "t.py", line 4, in myfunc 1/0 ZeroDivisionError: integer division or modulo by zero
Traceback (most recent call last): File "t.py", line 11, in <module> cursor.execute("select foo(1) from bar") File "apsw.c", line 3412, in resetcursor File "apsw.c", line 1597, in user-defined-scalar-foo File "t.py", line 4, in myfunc 1/0 ZeroDivisionError: integer division or modulo by zero
In the original traceback you can't even see that code in apsw was involved. The augmented traceback shows that there were indeed two function calls within apsw and gives you line numbers should you need to examine the code. Also note how you are told that the call was in user-defined-scalar-foo (ie you can tell which function was called.)
But wait, there is more!!! In order to further aid troubleshooting,
the augmented stack traces make additional information available. Each
frame in the traceback has local variables defined with more
information. You can use
print an exception with the local variables.
Here is a far more complex example from some virtual tables code I was writing. The BestIndex method in my code had returned an incorrect value. The augmented traceback includes local variables. I can see what was passed in to my method, what I returned and which item was erroneous. The original traceback is almost completely useless!
Traceback (most recent call last): File "tests.py", line 1387, in testVtables cursor.execute(allconstraints) TypeError: Bad constraint (#2) - it should be one of None, an integer or a tuple of an integer and a boolean
Augmented traceback with local variables:
Traceback (most recent call last): File "tests.py", line 1387, in testVtables cursor.execute(allconstraints) VTable = __main__.VTable cur = <apsw.Cursor object at 0x988f30> i = 10 self = testVtables (__main__.APSW) allconstraints = select rowid,* from foo where rowid>-1000 .... File "apsw.c", line 4050, in Cursor_execute.sqlite3_prepare Connection = <apsw.Connection object at 0x978800> statement = select rowid,* from foo where rowid>-1000 .... File "apsw.c", line 2681, in VirtualTable.xBestIndex self = <__main__.VTable instance at 0x98d8c0> args = (((-1, 4), (0, 32), (1, 8), (2, 4), (3, 64)), ((2, False),)) result = ([4, (3,), [2, False], , ], 997, u'\xea', False) File "apsw.c", line 2559, in VirtualTable.xBestIndex.result_constraint indices = [4, (3,), [2, False], , ] self = <__main__.VTable instance at 0x98d8c0> result = ([4, (3,), [2, False], , ], 997, u'\xea', False) constraint = (3,) TypeError: Bad constraint (#2) - it should be one of None, an integer or a tuple of an integer and a boolean