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# Exceptions

`apsw.Error` is the base for APSW exceptions.

exception `Error`

`Error.``result`

  For exceptions corresponding to SQLite error codes codes this attribute is the numeric error code.

`Error.``extendedresult`

  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 `result` would have the value `SQLITE_IOERR` while `extendedresult` would have the value `SQLITE_IOERR_SHORT_READ`.

## 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`

  See `apsw.fork_checker()`.

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 `Connection` or associated `cursors`.

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=?")

  Note

  It is not considered an error to have missing keys in a dictionary. For example this is perfectly valid:

      cursor.execute("insert into foo values($a,:b,$c)", {'a': 1})

  b and c are not in the dict. For missing keys, None/NULL will be used. This is so you don’t have to add lots of spurious values to the supplied dict. If your schema requires every column have a value, then SQLite will generate an error due to some values being None/NULL so that case will be caught.

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 `ExtensionLoadingError`

  An error happened loading an extension.

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.

## SQLite Exceptions

The following lists which Exception classes correspond to which SQLite error codes.

### General Errors

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.

### Internal Errors

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.

exception `RangeError`

  `SQLITE_RANGE`. (Cannot be generated using APSW). 2nd parameter to sqlite3_bind out of range

### Permissions Etc

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`

  `SQLITE_AUTH`. `Authorization` denied.

### Abort/Busy Etc

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 `Connection.interrupt()`.

exception `SchemaChangeError`

  `SQLITE_SCHEMA`. The database schema changed. A `prepared statement` becomes invalid if the database schema was changed. Behind the scenes SQLite reprepares the statement. Another or the same `Connection` may 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. If you have multiple constraints, you can’t tell which one was the cause.

### Memory/Disk

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 `Connection.limit()`.

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")

Original Traceback | Augmented Traceback
--- | ---

    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 print out the variables using ASPN recipe 52215

> In the recipe, the initial code in `print_exc_plus()` is far more complicated than need be, and also won’t work correctly with all tracebacks (it depends on `f_prev` being set which isn’t always the case). Change the function to start like this:

>     tb = sys.exc_info()[2]
>     stack = []

>     while tb:
>         stack.append(tb.tb_frame)
>         tb = tb.tb_next

>     traceback.print_exc()
>     print "Locals by frame, innermost last"

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 using recipe 52215. 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.

Original traceback:

    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], [1], [0]], 997, u'\xea', False)

      File "apsw.c", line 2559, in VirtualTable.xBestIndex.result_constraint
                   indices =  [4, (3,), [2, False], [1], [0]]
                      self =  <__main__.VTable instance at 0x98d8c0>
                    result =  ([4, (3,), [2, False], [1], [0]], 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

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