apsw.Error is the base for APSW exceptions.
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.
The following exceptions happen when APSW detects various problems.
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.
The following lists which Exception classes correspond to which SQLite error codes.
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 (all user defined function names are uppercased).
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