[sqlite3] Fetching an empty value from date column raises ValueError

[felixxm]

BPO	43752
Nosy	@berkerpeksag, @frenzymadness, @erlend-aasland, @felixxm
PRs	bpo-43752: Fix sqlite3 regression for zero-sized blobs with converters #25228

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-04-14.11:23:31.401>
created_at = <Date 2021-04-06.18:29:34.231>
labels = ['type-bug', 'library', '3.10']
title = '[sqlite3] Fetching an empty value from date column raises ValueError'
updated_at = <Date 2021-04-14.11:23:31.401>
user = 'https://github.com/felixxm'

bugs.python.org fields:

activity = <Date 2021-04-14.11:23:31.401>
actor = 'berker.peksag'
assignee = 'none'
closed = True
closed_date = <Date 2021-04-14.11:23:31.401>
closer = 'berker.peksag'
components = ['Library (Lib)']
creation = <Date 2021-04-06.18:29:34.231>
creator = 'felixxm'
dependencies = []
files = []
hgrepos = []
issue_num = 43752
keywords = ['patch']
message_count = 7.0
messages = ['390357', '390359', '390365', '390366', '390367', '391058', '391060']
nosy_count = 4.0
nosy_names = ['berker.peksag', 'frenzy', 'erlendaasland', 'felixxm']
pr_nums = ['25228']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43752'
versions = ['Python 3.10']

[felixxm]

We noticed a regression in Python3.10.0a7 (it works properly in Python3.10.0a6) when running Django's test suite. convert_date()[1] is called and crashes when fetching an empty value from date column on SQLite:

File "python3.10/lib/sqlite3/dbapi2.py", line 64, in convert_date
return datetime.date(*map(int, val.split(b"-")))
ValueError: invalid literal for int() with base 10: b''

I will bisect a regression and submit PR.

[1]

cpython/Lib/sqlite3/dbapi2.py

Lines 63 to 64 in 5061622

	def convert_date(val):
	return datetime.date(*map(int, val.split(b"-")))

[felixxm]

A regression test:

    def test_convert_null_date(self):
        con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_DECLTYPES)
        cur = con.cursor()
        cur.execute("CREATE TABLE t (x DATE NULL)")
        cur.execute("INSERT INTO t (x) VALUES (NULL)")
        cur.execute("SELECT * FROM t")
        values = [x[0] for x in cur.fetchall()]
        self.assertEqual(values, [None])

[erlend-aasland]

Thanks for the report and the test case! :)

Regression was introduced by e161ec5, where it was assumed that the handling of zero-sized blobs should be consistent. Unfortunately, the handling of zero-sized blobs is not consistent. Zero-sized blobs _with_ converters must return None; zero-sized blobs _without_ converters must return b"".

[erlend-aasland]

BTW, you might be interested in this bpo, Mariusz: bpo-43553

[erlend-aasland]

Zero-sized blobs _with_ converters must return None; zero-sized blobs _without_ converters must return b"".

Maybe the docs should be updated to reflect this inconsistency.

[berkerpeksag]

New changeset 6f1e8cc by Erlend Egeberg Aasland in branch 'master':
bpo-43752: Fix sqlite3 regression for zero-sized blobs with converters (GH-25228)
6f1e8cc

[berkerpeksag]

Thank you for the report and reproducer, Mariusz and thank you for the PR, Erlend.