assertion failure at Modules/_sqlite/blob.c:146: PyObject *read_multiple(pysqlite_Blob *, Py_ssize_t, Py_ssize_t): Assertion 'offset < sqlite3_blob_bytes(self->blob)' failed

Crash report

What happened?

import sqlite3

# 1. Setup an in-memory database with a BLOB column
con = sqlite3.connect(':memory:')
con.execute('create table test(b blob)')

# 2. Insert a small amount of data.
# The unicode character '\u2603' (Snowman) is 3 bytes in UTF-8 (b'\xe2\x98\x83').
# The blob size will be 3.
con.execute('insert into test(b) values (?)', ('\u2603',))

# 3. Open the BLOB for incremental I/O
# Table: 'test', Column: 'b', Row: 1
blob = con.blobopen('test', 'b', 1)

# 4. Trigger the crash
# We request a slice starting at index 5 (which is beyond the blob size of 3)
# and ending at index -5 (which wraps around to before the start).
# This combination causes the internal 'offset' calculation in C to assert
# failing that the offset (5) is not less than the blob bytes (3).
blob[5:-5]

python: ../Modules/_sqlite/blob.c:146: PyObject *read_multiple(pysqlite_Blob *, Py_ssize_t, Py_ssize_t): Assertion `offset < sqlite3_blob_bytes(self->blob)' failed.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

No response

Linked PRs

pythongh-142787: Fix assertion failure in sqlite3 blob slice

Add regression test for pythongh-142787

gh-142787: Handle empty sqlite3 blob slices (#142824)

pythongh-142787: Handle empty sqlite3 blob slices (pythonGH-142824)

[3.14] gh-142787: Handle empty sqlite3 blob slices (GH-142824) (#145297)

[3.13] gh-142787: Handle empty sqlite3 blob slices (GH-142824) (#145298)

@YuanchengJiang

Thanks for the report, @YuanchengJiang, and thanks for the fix @abdoulrasheed!

pythongh-142787: Handle empty sqlite3 blob slices (python#142824)

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assertion failure at Modules/_sqlite/blob.c:146: `PyObject read_multiple(pysqlite_Blob , Py_ssize_t, Py_ssize_t): Assertion 'offset < sqlite3_blob_bytes(self->blob)' failed` #142787

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assertion failure at Modules/_sqlite/blob.c:146: PyObject *read_multiple(pysqlite_Blob *, Py_ssize_t, Py_ssize_t): Assertion 'offset < sqlite3_blob_bytes(self->blob)' failed #142787

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Crash report

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CPython versions tested on:

Operating systems tested on:

Output from running 'python -VV' on the command line:

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erlend-aasland commented on Feb 27, 2026

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assertion failure at Modules/_sqlite/blob.c:146: `PyObject read_multiple(pysqlite_Blob , Py_ssize_t, Py_ssize_t): Assertion 'offset < sqlite3_blob_bytes(self->blob)' failed` #142787