Re: [sqlite] Differentiate between an empty result set and an error using Python3
>Possibly the Python documentation is overwhelming here as data can also be
>retrieved with explicit fetch steps.
The APSW documentation is better. The sqlite3 documentation is somewhat
limited.
>>> import sqlite3
>>> db = sqlite3.connect('', isolation_level=None) # isolation_level=None turns
>>> off automagic which does not work anyway
>>> db.execute('create table x(x)')
.fetchone() returns None if there is no rows, else it returns the row tuple:
>>> print(db.execute('select x from x').fetchone())
None
.fetchall() returns an list of rows (which will be empty if there are no rows):
>>> print(db.execute('select x from x').fetchall())
[]
Calling the iterator step function manually will throw StopIteration if there
are no more rows (that is how "for row in iter(...)" knows to stop iterating --
the for catches the StopIteration exception and stops executing the loop):
>>> print(next(db.execute('select x from x')))
Traceback (most recent call last):
File "", line 1, in
StopIteration
>>> print(db.execute('select x from x').__next__())
Traceback (most recent call last):
File "", line 1, in
StopIteration
APSW works the same way. https://github.com/rogerbinns/apsw
>>> import apsw
>>> db = apsw.Connection('')
>>> db.cursor().execute('create table x(x)')
>>> print(db.cursor().execute('select x from x').fetchone())
None
>>> print(db.cursor().execute('select x from x').fetchall())
[]
>>> print(next(db.cursor().execute('select x from x')))
Traceback (most recent call last):
File "", line 1, in
StopIteration
>>> print(db.cursor().execute('select x from x').__next__())
Traceback (most recent call last):
File "", line 1, in
StopIteration
--
The fact that there's a Highway to Hell but only a Stairway to Heaven says a
lot about anticipated traffic volume.
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Re: [sqlite] Differentiate between an empty result set and an error using Python3
> Op 5 sep. 2019, om 00:10 heeft Keith Medcalf het
> volgende geschreven:
>
>
> On Wednesday, 4 September, 2019 12:18, Rob Sciuk wrote:
>
>> Forgive me if this is an FAQ, but in looking over the python3 interface to
>> SQLITE3, I cannot see a way to get the result code (SQLITE_OK) after an
>> execute() command.
>
>> My use case is to differentiate between an empty row set (OK) vs an error
>> of some kind in the query.
>
>> Anyone figured this out?
>
> If there is an error then an exception will be thrown. No exception means no
> error. Otherwise, iterating over the cursor will return the rows. If there
> are no rows then it is like iterating over an empty list -- there is nothing
> to return (the cursor object is a generator that yields row tuples and it
> will internally raise StopIteration when it is out of data to return, just
> like any other generator).
>
> --
Possibly the Python documentation is overwhelming here as data can also be
retrieved with explicit fetch steps. The example where the cursor is treated as
a generator shows how simple it is:
>>> for row in c.execute('SELECT * FROM stocks ORDER BY price'):
print(row)
('2006-01-05', 'BUY', 'RHAT', 100, 35.14)
('2006-03-28', 'BUY', 'IBM', 1000, 45.0)
('2006-04-06', 'SELL', 'IBM', 500, 53.0)
('2006-04-05', 'BUY', 'MSFT', 1000, 72.0)
(from https://docs.python.org/3/library/sqlite3.html
)
Personal note: even more simple is to use the execute method directly from the
connection instance.
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Re: [sqlite] Differentiate between an empty result set and an error using Python3
On Wednesday, 4 September, 2019 12:18, Rob Sciuk wrote: >Forgive me if this is an FAQ, but in looking over the python3 interface to >SQLITE3, I cannot see a way to get the result code (SQLITE_OK) after an >execute() command. >My use case is to differentiate between an empty row set (OK) vs an error >of some kind in the query. >Anyone figured this out? If there is an error then an exception will be thrown. No exception means no error. Otherwise, iterating over the cursor will return the rows. If there are no rows then it is like iterating over an empty list -- there is nothing to return (the cursor object is a generator that yields row tuples and it will internally raise StopIteration when it is out of data to return, just like any other generator). -- The fact that there's a Highway to Hell but only a Stairway to Heaven says a lot about anticipated traffic volume. ___ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Differentiate between an empty result set and an error using Python3
If you run a query that returns no results, then cursor.fetchone() will return None, or cursor.fetchall() will return an empty list. If there is an error during the processing then some sort of exception should be raised. -Original Message- From: sqlite-users On Behalf Of Rob Sciuk Sent: Wednesday, September 04, 2019 2:18 PM To: sqlite-users@mailinglists.sqlite.org Subject: [sqlite] Differentiate between an empty result set and an error using Python3 Forgive me if this is an FAQ, but in looking over the python3 interface to SQLITE3, I cannot see a way to get the result code (SQLITE_OK) after an execute() command. My use case is to differentiate between an empty row set (OK) vs an error of some kind in the query. Anyone figured this out? Cheers, Rob. -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Robert S. Sciuk r...@controlq.com Principal Consultant905.706.1354 Control-Q Research 97 Village Rd. Wellesley, ON N0B 2T0 ___ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users ___ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
[sqlite] Differentiate between an empty result set and an error using Python3
Forgive me if this is an FAQ, but in looking over the python3 interface to SQLITE3, I cannot see a way to get the result code (SQLITE_OK) after an execute() command. My use case is to differentiate between an empty row set (OK) vs an error of some kind in the query. Anyone figured this out? Cheers, Rob. -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Robert S. Sciuk r...@controlq.com Principal Consultant905.706.1354 Control-Q Research 97 Village Rd. Wellesley, ON N0B 2T0 ___ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
