I am running the following script:

------------------------------------------
>>> import sqlite3
>>> import os
>>> import time
>>> con1 = sqlite3.connect("/tmp/test.db")
>>> con2 = sqlite3.connect("/tmp/test.db")
>>> con1.set_trace_callback(print)
>>> cur = con1.cursor()
>>> cur.execute("create table test(a)")
create table test(a)
<sqlite3.Cursor object at 0x7fb488ddf260>
>>> con2.execute("create table test2(a)")
<sqlite3.Cursor object at 0x7fb488ddf2d0>
>>> cur.execute("insert into test(a) values(1)")
BEGIN 
insert into test(a) values(1)
insert into test(a) values(1)
<sqlite3.Cursor object at 0x7fb488ddf260>
>>> for a in con1.execute("select * from test"):
...     print("result:", a)
... 
select * from test
result: (1,)
-------------------------------------------

As you can see i get duplicate traceback print of the "insert into test(a) values(1)" line. The duplicate print has no effect on the actual db.

I have tested this both on python 3.4.3 and 3.6.0a0 on ubuntu14.04

This issue will be resolved when we change the sqlite3_prepare to sqlite3_prepare_v2. So there should be a dependency on issue 9303.

It would be nice to add a test case to https://github.com/python/cpython/blob/86a670543ff97d52fd9b8ca0477f8b6d27ee946d/Lib/sqlite3/test/hooks.py#L204 before closing this.

I can work on this.

New changeset 0e6cb2ea624570ed08c354f1ed1f595dab4192d6 by Berker Peksag (Aviv Palivoda) in branch 'master':
bpo-26187: Test that set_trace_callback() is not called multiple times (GH-461)
https://github.com/python/cpython/commit/0e6cb2ea624570ed08c354f1ed1f595dab4192d6

Thanks, Anish and Aviv!