The sqlite3 context manager does not work with isolation_level=None #61162

bitdancer · 2013-01-14T00:46:44Z

BPO	16958
Nosy	@loewis, @bitdancer, @Kodiologist, @corona10, @coleifer, @erlend-aasland

^{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 = None
created_at = <Date 2013-01-14.00:46:44.408>
labels = ['extension-modules', 'type-bug', 'library']
title = 'The sqlite3 context manager does not work with isolation_level=None'
updated_at = <Date 2022-03-29.16:07:14.645>
user = 'https://github.com/bitdancer'

bugs.python.org fields:

activity = <Date 2022-03-29.16:07:14.645>
actor = 'corona10'
assignee = 'ghaering'
closed = False
closed_date = None
closer = None
components = ['Extension Modules', 'Library (Lib)']
creation = <Date 2013-01-14.00:46:44.408>
creator = 'r.david.murray'
dependencies = []
files = []
hgrepos = []
issue_num = 16958
keywords = []
message_count = 8.0
messages = ['179909', '179912', '179913', '219866', '248822', '348633', '349507', '415999']
nosy_count = 9.0
nosy_names = ['loewis', 'ghaering', 'r.david.murray', 'nagylzs', 'aymeric.augustin', 'Kodiologist', 'corona10', 'coleifer', 'erlendaasland']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue16958'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3', 'Python 3.4']

bitdancer · 2013-01-14T00:46:40Z

Its operation is also not particularly intuitive if isolation_level is not None, so its documentation needs some clarification.

Currently the transaction manager does nothing on enter, and does a commit or rollback on exit, depending on whether or not there was an exception inside the with block. With isolation_level set to None, the sqlite3 library is in autocommit mode, so changes will get committed immediately inside the with, which is simply broken.

If isolation_level is not None, then the behavior of the transaction manager depends heavily on what happens inside the with block. If the with block contains only the defined DQL statements (insert, update, delete, replace) and select statements, then things will work as expected. However, if another statement (such as a CREATE TABLE or a PRAGMA) is included in the with block, an intermediate commit will be done and a new transaction started.

I propose to do two things to fix this issue: explain the above in the transactions manager docs, and have the context manager check to see if we are in isolation_level None, and if so, issue a begin (and then document that as well).

One question is, can the fix be backported? It will change the behavior of code that doesn't throw an error, but most such code won't be doing what the author expected (run the with block inside a transaction...in pure autocommit mode the transaction manager is a no-op). One place code could break is if someone figured out this issue and worked around it by explicitly starting a transaction before (or after) entering the with block. In this case they would now get an error that a transaction cannot be started inside another. I would think this is unlikely...the more obvious workaround would be to write a custom transaction manager, so I suspect that that is what is actually in the field. But that's a (hopeful :) guess.

A fix for this problem would be to use 'savepoint' instead of 'begin' if the sqlite3 version supports it (it is apparently supported as of 3.6.8).

So, I'd like to see the fix, conditionally using SAVEPOINT, (once it written and tested) applied to all active python versions, but am open to the argument that it shouldn't be.

loewis · 2013-01-14T01:04:11Z

"changes will get committed immediately inside the with, which is simply broken"

What do you mean by that?
A. Changes ought to be committed immediately, but are not; it is broken, and changes must be committed immediately.

or -
B. What actually happens is that changes are committed immediately, and sqlite is incorrect in doing so.

Your discussion suggests B; in this case, I disagree that there is a bug. In auto-commit mode, it should really auto-commit, regardless of context managers. The context manager documentation doesn't claim otherwise.

bitdancer · 2013-01-14T01:15:51Z

B, yes.

So you would view the connection context manager acting as an actual transaction manager as a new feature? Would you be OK with adding that feature to the existing context manager in 3.4 (since currently the context manager is a noop in autocommit mode), or do you think we need to create a new context manager for this? Or do we do as the issue that sparked this (bpo-8145) suggested, and just document how to create your own?

aymericaugustin · 2014-06-06T09:45:26Z

Thesis *

I belive that using the connection as a context manager is an inadequate API for controlling transactions because it's very likely to result in subtly broken code.

As a consequence, my recommendation would be to deprecate this API.

Argumentation *

If you nest a naive transaction context manager (BEGIN / COMMIT / ROLLBACK), you'll get very lousy transaction semantics. Look at this example:

with connection:   # outer transaction

    with connection:   # inner transaction
        do_X_in_db()

    do_Y_in_db()

# once in a while, you get an exception there...

With this code, when you get an exception, X will be presevred in the database, but not Y. Most likely this breaks the expectations of the "outer transaction". Now, imagine the inner transaction in deep inside a third-party library, and you understand that this API is a Gun Pointed At Feet.

Of course, you could say "don't nest", but:

this clashes with the expected semantics of Python context managers,
it's unreasonable to expect Python users to audit all their lower level libraries for this issue!

Now, let's look at how popular database-oriented libraires handle this.

SQLAlchemy provides an explicit begin() method: http://docs.sqlalchemy.org/en/latest/core/connections.html#sqlalchemy.engine.Connection.begin

It also provides variants for nested transactions and two-phase commits.

Django provide an all-purpose atomic() context manager:
https://docs.djangoproject.com/en/stable/topics/db/transactions/#django.db.transaction.atomic

That function takes a keyword argument, savepoint, to control whether a savepoint is emitted for nested transactions.

So it's possible to implement a safe, nestable context manager with savepoints. However:

you need to provide more control, and as a consequence you cannot simply use the connection as a context manager anymore;
it takes a lot of rather complex code. See Django's implementation for an example:
https://github.com/django/django/blob/stable/1.6.x/django/db/transaction.py#L199-L372

If you ignore the cross-database compatibility stuff, you're probably still looking at over a hundred lines of very stateful code...

That's why I believe it's better to leave this up to user code, and to stop providing an API that looks good for trivial use cases but that's likely to introduce subtle transactional integrity bugs.

ghaering · 2015-08-19T09:34:18Z

I'm +1 on deprecating the connection manager

vstinner · 2019-07-29T11:46:09Z

This issue is no newcomer friendly, I remove the "easy" keyword.

coleifer · 2019-08-12T23:23:06Z

With isolation_level set to None, the sqlite3 library is in autocommit mode, so changes will get committed immediately inside the with, which is simply broken.

Not necessarily. When sqlite is in autocommit mode, you can still open transactions by executing a BEGIN query. In fact, that's the main reason to use isolation_level=None -- you can manage the transactions yourself.

Kodiologist · 2022-03-25T14:12:40Z

This bit me real bad. On Python 3.8, I wrote a program with isolation_level = None and with db: … and spent a long time figuring out why writes were so slow. Turns out that with db doesn't actually start a transaction in this case, as the documentation suggests it should. This issue is approaching the age of 10, so if there's still uncertainty about how the implementation or the interface should change, the docs should be clarified in the meantime.

I always thought the Python library turning off autocommit by default, contrary to SQLite's command-line interface, was needlessly surprising. I think it contributed to this problem because the docs about context managers seem to assume you have autocommit off.

erlend-aasland · 2022-06-16T07:50:00Z

I'm not sure we should change the current context manager to emit BEGIN statements on enter. That could be backwards incompatible.

I think the best solution may be to deprecate the current context manager, and possibly introduce a new SAVEPOINT based context manager that allows nesting.

cx = sqlite3.connect(":memory:")
with cx.savepoint("sp1"):
    with cx.savepoint("sp2"):
        pass

# alternatively, we could auto-generate savepoint names internally
with cx.savepoint():
    with cx.savepoint():
        pass

If we can land a new PEP-249-compliant transaction behaviour (gh-83638), the existing context manager will behave like this:

autocommit=False; a transaction is always open, so there will be no need to execute BEGIN on __enter__; exit will work as before and commit/rollback.
autocommit=True; transaction handling is left to SQLite's autocommit mode (or any explicit transaction handling performed by the user); the existing context manager is a no-op (this will be documented).

Explicitly note that transactions are only closed if there is an open transation, and that transactions are _not_ implicitly opened in context manager __enter__.

erlend-aasland · 2022-06-16T08:12:43Z

@Kodiologist:

the docs should be clarified in the meantime.

See gh-93890

Explicitly note that transactions are only closed if there is an open transation at `__exit__`, and that transactions are not implicitly opened during `__enter__`. Co-authored-by: CAM Gerlach <CAM.Gerlach@Gerlach.CAM> Co-authored-by: Stanley <46876382+slateny@users.noreply.github.com> Automerge-Triggered-By: GH:erlend-aasland

…onGH-93890) Explicitly note that transactions are only closed if there is an open transation at `__exit__`, and that transactions are not implicitly opened during `__enter__`. Co-authored-by: CAM Gerlach <CAM.Gerlach@Gerlach.CAM> Co-authored-by: Stanley <46876382+slateny@users.noreply.github.com> Automerge-Triggered-By: GH:erlend-aasland (cherry picked from commit 8e08978) Co-authored-by: Erlend Egeberg Aasland <erlend.aasland@protonmail.com>

erlend-aasland · 2022-06-19T20:21:35Z

The docs are now updated in:

main: gh-61162: Clarify sqlite3 connection context manager docs #93890
3.11: [3.11] gh-61162: Clarify sqlite3 connection context manager docs (GH-93890) #94013
3.10: [3.10] gh-61162: Clarify sqlite3 connection context manager docs (GH-93890) #94012

Explicitly note that transactions are only closed if there is an open transation at `__exit__`, and that transactions are not implicitly opened during `__enter__`. Co-authored-by: CAM Gerlach <CAM.Gerlach@Gerlach.CAM> Co-authored-by: Stanley <46876382+slateny@users.noreply.github.com> Automerge-Triggered-By: GH:erlend-aasland (cherry picked from commit 8e08978) Co-authored-by: Erlend Egeberg Aasland <erlend.aasland@protonmail.com>

erlend-aasland · 2022-06-19T20:31:01Z

IMO, we can close this issue now.

I think the discussion of deprecating the current context manager and/or possibly replacing it with a new SAVEPOINT-based context manager should have a wider audience than this issue alone. I therefore suggest opening a topic on Discourse, to try and gain more attention to such changes. If there is sufficient interest in following up and implementing the deprecation and/or a new context manager, I suggest we create new issue on the bug tracker, with backlinks to this discussion for reference.

@brettcannon

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(GH-93673) * GH-93516: Store offset of first traceable instruction in code object (GH-93769) * gh-90473: Include stdlib dir in wasmtime PYTHONPATH (GH-93797) * GH-93429: Merge `LOAD_METHOD` back into `LOAD_ATTR` (GH-93430) * gh-93353: regrtest checks for leaked temporary files (#93776) When running tests with -jN, create a temporary directory per process and mark a test as "environment changed" if a test leaks a temporary file or directory. * gh-79579: Improve DML query detection in sqlite3 (#93623) The fix involves using pysqlite_check_remaining_sql(), not only to check for multiple statements, but now also to strip leading comments and whitespace from SQL statements, so we can improve DML query detection. pysqlite_check_remaining_sql() is renamed lstrip_sql(), to more accurately reflect its function, and hardened to handle more SQL comment corner cases. * GH-93678: reduce boilerplate and code repetition in the compiler (GH-93682) * gh-91877: Fix WriteTransport.get_write_buffer_{limits,size} docs (#92338) - Amend docs for WriteTransport.get_write_buffer_limits - Add docs for WriteTransport.get_write_buffer_size * GH-93429: Document `LOAD_METHOD` removal (GH-93803) * Include freelists in allocation total. (GH-93799) * gh-93795: Use test.support TESTFN/unlink in sqlite3 tests (#93796) * Remove LOAD_METHOD stats. (GH-93807) * Rename 'LOAD_METHOD' specialization stat consts to 'ATTR'. (GH-93812) * gh-93353: Fix regrtest for -jN with N >= 2 (GH-93813) * [docs] Fix LOAD_ATTR version changed (GH-93816) * gh-93814: Add infinite test for itertools.chain.from_iterable (GH-93815) fix #93814 Automerge-Triggered-By: GH:rhettinger * gh-93735: Split Docs CI to speed-up the build (GH-93736) * gh-93183: Adjust wording in socket docs (#93832) package => packet Co-authored-by: Victor Norman * gh-93829: In sqlite3, replace Py_BuildValue with faster APIs (#93830) - In Modules/_sqlite/connection.c, use PyLong_FromLong - In Modules/_sqlite/microprotocols.c, use PyTuple_Pack * Add test.support.busy_retry() (#93770) Add busy_retry() and sleeping_retry() functions to test.support. * gh-87260: Update sqlite3 signature docs to reflect actual implementation (#93840) Align the docs for the following methods with the actual implementation: - sqlite3.complete_statement() - sqlite3.Connection.create_function() - sqlite3.Connection.create_aggregate() - sqlite3.Connection.set_progress_handler() * test_thread uses support.sleeping_retry() (#93849) test_thread.test_count() now fails if it takes longer than LONG_TIMEOUT seconds. * Use support.sleeping_retry() and support.busy_retry() (#93848) * Replace time.sleep(0.010) with sleeping_retry() to use an exponential sleep. * support.wait_process(): reuse sleeping_retry(). * _test_eintr: remove unused variables. * Update includes in call.c (GH-93786) * gh-93857: Fix broken audit-event targets in sqlite3 docs (#93859) Corrected targets for the following audit-events: - sqlite3.enable_load_extension => sqlite3.Connection.enable_load_extension - sqlite3.load_extension => sqlite3.Connection.load_extension * GH-93850: Fix test_asyncio exception ignored tracebacks (#93854) * gh-93824: Reenable installation of shell extension on Windows ARM64 (GH-93825) * test_asyncio: run_until() implements exponential sleep (#93866) run_until() of test.test_asyncio.utils now uses an exponential sleep delay (max: 1 second), rather than a fixed delay of 1 ms. Similar design than support.sleeping_retry() wait strategy that applies exponential backoff. * test_asyncore: Optimize capture_server() (#93867) Remove time.sleep(0.01) in test_asyncore capture_server(). The sleep was redundant and inefficient, since the loop starts with select.select() which also implements a sleep (poll for socket data with a timeout). * Tests call sleeping_retry() with SHORT_TIMEOUT (#93870) Tests now call busy_retry() and sleeping_retry() with SHORT_TIMEOUT or LONG_TIMEOUT (of test.support), rather than hardcoded constants. Add also WAIT_ACTIVE_CHILDREN_TIMEOUT constant to _test_multiprocessing. * gh-84461: Document how to install SDKs manually (GH-93844) Co-authored-by: Brett Cannon <brett@python.org> * gh-93820: Fix copy() regression in enum.Flag (GH-93876) GH-26658 introduced a regression in copy / pickle protocol for combined `enum.Flag`s. `copy.copy(re.A | re.I)` would fail with `AttributeError: ASCII|IGNORECASE`. `enum.Flag` now has a `__reduce_ex__()` method that reduces flags by combined value, not by combined name. * Call busy_retry() and sleeping_retry() with error=True (#93871) Tests no longer call busy_retry() and sleeping_retry() with error=False: raise an exception if the loop times out. * gh-87347: Add parenthesis around PyXXX_Check() arguments (#92815) * gh-91321: Fix test_cppext for C++03 (#93902) Don't build _testcppext.cpp with -Wzero-as-null-pointer-constant when testing C++03: only use this compiler flag with C++11. * gh-91577: SharedMemory move imports out of methods (#91579) SharedMemory.unlink() uses the unregister() function from resource_tracker. Previously it was imported in the method, but this can fail if the method is called during interpreter shutdown, for example when unlink is part of a __del__() method. Moving the import to the top of the file, means that the unregister() method is available during interpreter shutdown. The register call in SharedMemory.__init__() can also use this imported resource_tracker. * gh-92547: Amend What's New (#93872) * Fix BINARY_SUBSCR_GETITEM stats (GH-93903) * gh-93847: Fix repr of enum of generic aliases (GH-93885) * gh-93353: regrtest supports checking tmp files with -j2 (#93909) regrtest now also implements checking for leaked temporary files and directories when using -jN for N >= 2. Use tempfile.mkdtemp() to create the temporary directory. Skip this check on WASI. * GH-91389: Fix dis position information for CACHEs (GH-93663) * gh-91985: Ensure in-tree builds override platstdlib_dir in every path calculation (GH-93641) * GH-83658: make multiprocessing.Pool raise an exception if maxtasksperchild is not None or a positive int (GH-93364) Closes #83658. * test_logging: Fix BytesWarning in SysLogHandlerTest (GH-93920) * gh-91404: Revert "bpo-23689: re module, fix memory leak when a match is terminated by a signal or allocation failure (GH-32283) (#93882) Revert "bpo-23689: re module, fix memory leak when a match is terminated by a signal or memory allocation failure (GH-32283)" This reverts commit 6e3eee5. Manual fixups to increase the MAGIC number and to handle conflicts with a couple of changes that landed after that. Thanks for reviews by Ma Lin and Serhiy Storchaka. * gh-89745: Avoid exact match when comparing program_name in test_embed on Windows (GH-93888) * gh-93852: Add test.support.create_unix_domain_name() (#93914) test_asyncio, test_logging, test_socket and test_socketserver now create AF_UNIX domains in the current directory to no longer fail with OSError("AF_UNIX path too long") if the temporary directory (the TMPDIR environment variable) is too long. Modify the following tests to use create_unix_domain_name(): * test_asyncio * test_logging * test_socket * test_socketserver test_asyncio.utils: remove unused time import. * gh-77782: Py_FdIsInteractive() now uses PyConfig.interactive (#93916) * gh-74953: Add _PyTime_FromMicrosecondsClamp() function (#93942) * gh-74953: Fix PyThread_acquire_lock_timed() code recomputing the timeout (#93941) Set timeout, don't create a local variable with the same name. * gh-77782: Deprecate global configuration variable (#93943) Deprecate global configuration variable like Py_IgnoreEnvironmentFlag: the Py_InitializeFromConfig() API should be instead. Fix declaration of Py_GETENV(): use PyAPI_FUNC(), not PyAPI_DATA(). * gh-93911: Specialize `LOAD_ATTR_PROPERTY` (GH-93912) * gh-92888: Fix memoryview bad `__index__` use after free (GH-92946) Co-authored-by: chilaxan <35645806+chilaxan@users.noreply.github.com> Co-authored-by: Serhiy Storchaka <3659035+serhiy-storchaka@users.noreply.github.com> * GH-89858: Fix test_embed for out-of-tree builds (GH-93465) * gh-92611: Add details on replacements for cgi utility funcs (GH-92792) Per @brettcannon 's [suggestions on the Discourse thread](https://discuss.python.org/t/pep-594-take-2-removing-dead-batteries-from-the-standard-library/13508/51), discussed in #92611 and as a followup to PR #92612 , this PR add additional specific per-function replacement information for the utility functions in the `cgi` module deprecated by PEP 594 (PEP-594). @brettcannon , should this be backported (without the `deprecated-removed` , which I would update it accordingly and re-add in my other PR adding that to the others for 3.11+), or just go in 3.11+? * GH-77403: Fix tests which fail when PYTHONUSERBASE is not normalized (GH-93917) * gh-91387: Strip trailing slash from tarfile longname directories (GH-32423) Co-authored-by: Brett Cannon <brett@python.org> * Add jaraco as primary owner of importlib.metadata and importlib.resources. (#93960) * Add jaraco as primary owner of importlib.metadata and importlib.resources. * Align indentation. Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com> Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com> * gh-84461: Fix circulare dependency on BUILDPYTHON (GH-93977) * gh-89828: Do not relay the __class__ attribute in GenericAlias (#93754) list[int].__class__ returned type, and isinstance(list[int], type) returned True. It caused numerous problems in code that checks isinstance(x, type). * gh-84461: Fix pydebug Emscripten browser builds (GH-93982) wasm_assets script did not take the ABIFLAG flag of sysconfigdata into account. * gh-93955: Use unbound methods for slot `__getattr__` and `__getattribute__` (GH-93956) * gh-91387: Fix tarfile test on WASI (GH-93984) WASI's rmdir() syscall does not like the trailing slash. * gh-93975: Nicer error reporting in test_venv (GH-93959) - gh-93957: Provide nicer error reporting from subprocesses in test_venv.EnsurePipTest.test_with_pip. - Update changelog This change does three things: 1. Extract a function for trapping output in subprocesses. 2. Emit both stdout and stderr when encountering an error. 3. Apply the change to `ensurepip._uninstall` check. * GH-93990: fix refcounting bug in `add_subclass` in `typeobject.c` (GH-93989) * What's new in 3.10: fix link to issue (#93968) * What's new in 3.10: fix link to issue * What's new in 3.10: fix link to GH issue Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com> Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com> * gh-93761: Fix test_logging test_config_queue_handler() race condition (#93952) Fix a race condition in test_config_queue_handler() of test_logging. * gh-74953: Reformat PyThread_acquire_lock_timed() (#93947) Reformat the pthread implementation of PyThread_acquire_lock_timed() using a mutex and a conditioinal variable. * Add goto to avoid multiple indentation levels and exit quickly * Use "while(1)" and make the control flow more obvious. * PEP 7: Add braces around if blocks. * gh-93937, C API: Move PyFrame_GetBack() to Python.h (#93938) Move the follow functions and type from frameobject.h to pyframe.h, so the standard <Python.h> provide frame getter functions: * PyFrame_Check() * PyFrame_GetBack() * PyFrame_GetBuiltins() * PyFrame_GetGenerator() * PyFrame_GetGlobals() * PyFrame_GetLasti() * PyFrame_GetLocals() * PyFrame_Type Remove #include "frameobject.h" from many C files. It's no longer needed. * gh-93991: Use boolean instead of 0/1 for condition check (GH-93992) # gh-93991: Use boolean instead of 0/1 for condition check * gh-84461: Fix Emscripten umask and permission issues (GH-94002) - Emscripten's default umask is too strict, see emscripten-core/emscripten#17269 - getuid/getgid and geteuid/getegid are stubs that always return 0 (root). Disable effective uid/gid syscalls and fix tests that use chmod() current user. - Cannot drop X bit from directory. * gh-84461: Skip test_unwritable_directory again on Emscripten (GH-94007) GH-93992 removed geteuid() and enabled the test again on Emscripten. * gh-93925: Improve clarity of sqlite3 commit/rollback, and close docs (#93926) Co-authored-by: CAM Gerlach <CAM.Gerlach@Gerlach.CAM> * gh-61162: Clarify sqlite3 connection context manager docs (GH-93890) Explicitly note that transactions are only closed if there is an open transation at `__exit__`, and that transactions are not implicitly opened during `__enter__`. Co-authored-by: CAM Gerlach <CAM.Gerlach@Gerlach.CAM> Co-authored-by: Stanley <46876382+slateny@users.noreply.github.com> Automerge-Triggered-By: GH:erlend-aasland * gh-79009: sqlite3.iterdump now correctly handles tables with autoincrement (#9621) Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com> * gh-84461: Silence some compiler warnings on WASM (GH-93978) * GH-93897: Store frame size in code object and de-opt if insufficient space on thread frame stack. (GH-93908) * GH-93516: Speedup line number checks when tracing. (GH-93763) * Use a lookup table to reduce overhead of getting line numbers during tracing. * gh-90539: doc: Expand on what should not go into CFLAGS, LDFLAGS (#92754) * gh-87347: Add parenthesis around macro arguments (#93915) Add unit test on Py_MEMBER_SIZE() and some other macros. * gh-93937: PyOS_StdioReadline() uses PyConfig.legacy_windows_stdio (#94024) On Windows, PyOS_StdioReadline() now gets PyConfig.legacy_windows_stdio from _PyOS_ReadlineTState, rather than using the deprecated global Py_LegacyWindowsStdioFlag variable. Fix also a compiler warning in Py_SetStandardStreamEncoding(). * GH-93249: relax overly strict assertion on bounds->ar_start (GH-93961) * gh-94021: Address unreachable code warning in specialize code (GH-94022) * GH-93678: refactor compiler so that optimizer does not need the assembler and compiler structs (GH-93842) * gh-93839: Move Lib/ctypes/test/ to Lib/test/test_ctypes/ (#94041) * Move Lib/ctypes/test/ to Lib/test/test_ctypes/ * Remove Lib/test/test_ctypes.py * Update imports and build system. * gh-93839: Move Lib/unttest/test/ to Lib/test/test_unittest/ (#94043) * Move Lib/unittest/test/ to Lib/test/test_unittest/ * Remove Lib/test/test_unittest.py * Replace unittest.test with test.test_unittest * Remove unittest.load_tests() * Rewrite unittest __init__.py and __main__.py * Update build system, CODEOWNERS, and wasm_assets.py * GH-91432: Specialize FOR_ITER (GH-91713) * Adds FOR_ITER_LIST and FOR_ITER_RANGE specializations. * Adds _PyLong_AssignValue() internal function to avoid temporary boxing of ints. * gh-94028: Clear and reset sqlite3 statements properly in cursor iternext (GH-94042) * gh-94052: Don't re-run failed tests with --python option (#94054) * gh-93839: Use load_package_tests() for testmock (GH-94055) Fixes failing tests on WebAssembly platforms. Automerge-Triggered-By: GH:tiran * gh-54781: Move Lib/lib2to3/tests/ to Lib/test/test_lib2to3/ (#94049) * Move Lib/lib2to3/tests/ to Lib/test/test_lib2to3/. * Remove Lib/test/test_lib2to3.py. * Update imports. * all_project_files(): use different paths and sort files to make the tests more reproducible. * Update references to tests. * gh-74953: _PyThread_cond_after() uses _PyTime_t (#94056) pthread _PyThread_cond_after() implementation now uses the _PyTime_t type to handle properly overflow: clamp to the maximum value. Remove MICROSECONDS_TO_TIMESPEC() function. * GH-93841: Allow stats to be turned on and off, cleared and dumped at runtime. (GH-93843) * gh-86986: Drop compatibility support for Sphinx 2 (GH-93737) * Revert "bpo-42843: Keep Sphinx 1.8 and Sphinx 2 compatibility (GH-24282)" This reverts commit 5c1f15b * Revert "bpo-42579: Make workaround for various versions of Sphinx more robust (GH-23662)" This reverts commit b63a620. * gh-94068: Remove HVSOCKET_CONTAINER_PASSTHRU constant because it has been removed from Windows (GH-94069) Fixes #94068 Automerge-Triggered-By: GH:zware * Closes gh-94038: Update Release Schedule in README.rst from PEP 664 to PEP 693 (GH-94046) * gh-93851: Fix all broken links in Doc/ (GH-93853) * gh-93675: Fix typos in `Doc/` (GH-93676) Closes #93675 * Minor optimization for Fractions.limit_denominator (GH-93730) When we construct the upper and lower candidates in limit_denominator, the numerator and denominator are already relatively prime (and the denominator positive) by construction, so there's no need to go through the usual normalisation in the constructor. This saves a couple of potentially expensive gcd calls. Suggested by Michael Scott Asato Cuthbert in GH-93477. * gh-93240: clarify wording in IO tutorial (GH-93276) Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com> * Tutorial: specify match cases don't fall through (GH-93615) * gh-93021: Fix __text_signature__ for __get__ (GH-93023) Because of the way wrap_descr_get is written, the second argument to __get__ methods implemented through the wrapper is always optional. * gh-82927: Update files related to HTML entities. (GH-92504) * DOC: correct bytesarray -> bytearray in comments (GH-92410) * gh-87389: Fix an open redirection vulnerability in http.server. (#93879) Fix an open redirection vulnerability in the `http.server` module when an URI path starts with `//` that could produce a 301 Location header with a misleading target. Vulnerability discovered, and logic fix proposed, by Hamza Avvan (@hamzaavvan). Test and comments authored by Gregory P. Smith [Google]. * gh-89336: Remove configparser APIs that were deprecated for 3.12 (#92503) https://github.com/python/cpython/issue/89336: Remove configparser 3.12 deprecations. Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com> * bpo-30535: [doc] state that sys.meta_path is not empty by default (GH-94098) Co-authored-by: Windson yang <wiwindson@outlook.com> * gh-88123: Implement new Enum __contains__ (GH-93298) Co-authored-by: Ethan Furman <ethan@stoneleaf.us> * Stats: Add summary of top instructions for misses and deferred specialization. (GH-94072) * gh-74696: Do not change the current working directory in shutil.make_archive() if possible (GH-93160) It is no longer changed when create a zip or tar archive. It is still changed for custom archivers registered with shutil.register_archive_format() if root_dir is not None. Co-authored-by: Éric <merwok@netwok.org> Co-authored-by: Łukasz Langa <lukasz@langa.pl> * gh-94101 Disallow instantiation of SSLSession objects (GH-94102) Fixes #94101 Automerge-Triggered-By: GH:tiran * Fix typo in _io.TextIOWrapper Clinic input (#94037) Co-authored-by: Łukasz Langa <lukasz@langa.pl> * gh-93951: In test_bdb.StateTestCase.test_skip, avoid including auxiliary importers. (GH-93962) Co-authored-by: Brett Cannon <brett@python.org> * gh-91172: Create a workflow for verifying bundled pip and setuptools (GH-31885) Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com> Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com> * gh-94114: Remove obsolete reference to python.org mirrors (GH-94115) * gh-94114 * gh-84623: Remove unused imports (#94132) * gh-54781: Move Lib/tkinter/test/test_ttk/ to Lib/test/test_ttk/ (#94070) * Move Lib/tkinter/test/test_tkinter/ to Lib/test/test_tkinter/. * Move Lib/tkinter/test/test_ttk/ to Lib/test/test_ttk/. * Add Lib/test/test_ttk/__init__.py based on test_ttk_guionly.py. * Add Lib/test/test_tkinter/__init__.py * Remove old Lib/test/test_tk.py. * Remove old Lib/test/test_ttk_guionly.py. * Add __main__ sub-modules. * Update imports and update references to rename files. * gh-84623: Move imports in doctests (#94133) Move imports in doctests to prevent false alarms in pyflakes. * Add ABI dump Makefile target (#94136) * gh-84623: Remove unused imports in idlelib (#94143) Remove commented code in test_debugger_r.py. Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu> * gh-85308: argparse: Use filesystem encoding for arguments file (GH-93277) * Closes gh-94152: Update pyvideo.org URL (GH-94075) The URL is now https://pyvideo.org, which uses HTTPS and avoids a redirect. * gh-91456: [Enum] Deprecate default auto() behavior with mixed value types (GH-91457) When used with plain Enum, auto() returns the last numeric value assigned, skipping any incompatible member values (such as strings); starting in 3.13 the default auto() for plain Enums will require all the values to be of compatible types, and will return a new value that is 1 higher than any existing value. Co-authored-by: Ethan Furman <ethan@stoneleaf.us> * gh-84461: Fix test_sqlite for Emscripten/WASI (#94125) * gh-86404: [doc] Fix missing backtick and double target name. (#94120) * gh-89121: Keep the number of pending SQLite statements to a minimum (#30379) Make sure statements that have run to completion or errored are reset and cleared off the cursor for all paths in execute() and executemany(). * GH-91742: Fix pdb crash after jump (GH-94171) * [Enum] fix typo (GH-94158) * gh-92858: Improve error message for some suites with syntax error before ':' (#92894) * gh-93771: Clarify how deepfreeze.py is run (#94150) * gh-91219: Add an index_pages default list and parameter to SimpleHTTPRequestHandler (GH-31985) * Add an index_pages default list to SimpleHTTPRequestHandler and an optional constructor parameter that allows the default indexes pages list to be overridden. This makes it easy to set a new index page name without having to override send_head. * [Enum] Remove automatic docstring generation (GH-94188) * Add ABI dump script (#94135) * Add more tests for throwing into yield from (GH-94097) * gh-94169: Remove deprecated io.OpenWrapper (#94170) Remove io.OpenWrapper and _pyio.OpenWrapper, deprecated in Python 3.10: just use :func:`open` instead. The open() (io.open()) function is a built-in function. Since Python 3.10, _pyio.open() is also a static method. * gh-94199: Remove ssl.RAND_pseudo_bytes() function (#94202) Remove the ssl.RAND_pseudo_bytes() function, deprecated in Python 3.6: use os.urandom() or ssl.RAND_bytes() instead. * gh-94196: Remove gzip.GzipFile.filename attribute (#94197) gzip: Remove the filename attribute of gzip.GzipFile, deprecated since Python 2.6, use the name attribute instead. In write mode, the filename attribute added '.gz' file extension if it was not present. * gh-93692: remove "build finished successfully" message from setup.py (#93693) The message was only emitted when the build succeeded _and_ there were missing modules. * gh-84461: Fix ctypes and test_ctypes on Emscripten (#94142) - c_longlong and c_longdouble need experimental WASM bigint. - Skip tests that need threading - Define ``CTYPES_MAX_ARGCOUNT`` for Emscripten. libffi-emscripten 2022-06-23 supports up to 1000 args. * gh-94205: Ensures all required DLLs are copied on Windows for underpth tests (GH-94206) * gh-84461: Build Emscripten with WASM BigInt support (#94219) * gh-94172: urllib.request avoids deprecated check_hostname (#94193) The urllib.request no longer uses the deprecated check_hostname parameter of the http.client module. Add private http.client._create_https_context() helper to http.client, used by urllib.request. Remove the now redundant check on check_hostname and verify_mode in http.client: the SSLContext.check_hostname setter already implements the check. * IDLE: replace if statement with expression (#94228) * Docs: Remove `Provides [...]` from `multiprocessing.shared_memory` description (#92761) * gh-93382: Sync up `co_code` changes with 3.11 (GH-94227) Sync up co_code changes with 3.11 commit 852b4d4. * gh-94217: Skip import tests when _testcapi is a builtin (GH-94218) * gh-85308: Add argparse tests for reading non-ASCII arguments from file (GH-94160) * bpo-46642: Explicitly disallow subclassing of instaces of TypeVar, ParamSpec, etc (GH-31148) The existing test covering this case passed only incidentally. We explicitly disallow doing this and add a proper error message. Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> * bpo-26253: Add compressionlevel to tarfile stream (GH-2962) `tarfile` already accepts a compressionlevel argument for creating files. This patch adds the same for stream-based tarfile usage. The default is 9, the value that was previously hard-coded. * gh-70441: Fix test_tarfile on systems w/o bz2 (gh-2962) (#94258) * gh-94199: Remove ssl.match_hostname() function (#94224) * gh-94207: Fix struct module leak (GH-94239) Make _struct.Struct a GC type This fixes a memory leak in the _struct module, where as soon as a Struct object is stored in the cache, there's a cycle from the _struct module to the cache to Struct objects to the Struct type back to the module. If _struct.Struct is not gc-tracked, that cycle is never collected. This PR makes _struct.Struct GC-tracked, and adds a regression test. * gh-94245: Test pickling and copying of typing.Tuple[()] (GH-94259) * gh-77560: Report possible errors in restoring builtins at finalization (GH-94255) Seems in the past the copy of builtins was not made in some scenarios, and the error was silenced. Write it now to stderr, so we have a chance to see it. * gh-90016: Reword sqlite3 adapter/converter docs (#93095) Also add adapters and converter recipes. Co-authored-by: CAM Gerlach <CAM.Gerlach@Gerlach.CAM> Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com * bpo-39971: Change examples to be runnable (GH-32172) * gh-70474: [doc] fix wording of GET_ANEXT doc (GH-94048) * gh-93259: Validate arg to ``Distribution.from_name``. (GH-94270) Syncs with importlib_metadata 4.12.0. 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phiresky · 2022-07-15T11:42:19Z

I just hit the same issue as @Kodiologist

Specifically what happens:

First, you use sqlite3 library like this:

db = sqlite3.connect("x.db")
db.execute("create table foo(x);") # this auto-commits, as expected. `$ sqlite3 x.db .dump` shows the table as expected.
db.execute("insert into foo values (1);") # this implicitly creates a cursor and a transaction but doesn't commit it!!
db.close()
# $ sqlite3 x.db .dump # the table is empty! why?

After a while of thinking your code is buggy you find out that sqlite3 uses isolation_level=DEFERRED by default which starts a transaction "secretly" and is different than the default of the sqlite3 REPL (and pretty much every other database engine I've seen)

So you set isolation_level=None to get the behaviour you expected. But then some time later you write this code:

db = sqlite3.connect("x.db", isolation_level=None)

db.execute("insert into foo values (1);") # this one autocommits as expected
with db:
    for i in range(1000):
        db.execute("insert into foo values (1);")
        # i would expect these all to happen in one transaction, but turns out it commits after every insert
        # (you probably won't even realize this until later just thinking sqlite itself is slow)
    db.execute("syntax error")
    # the table contains the value that you think was rolled back
    # but it turns out `with db` doesn't actually do anything when isolation_mode=None

I think this behaviour is really confusing for most people, at least those coming from SQLite in different programming langugaes as well as other db engines like PostgreSQL.

Here's my workaround:

class ConnectionFixedCtxManager(sqlite3.Connection):
    def __enter__(self) -> ConnectionFixedCtxManager:
        raise Exception(
            "don't use contextmanager on sqlite3 connection, it's broken with isolation_level=None (which is the sane default). use .transaction() instead (see https://github.com/python/cpython/issues/61162)"
        )

    def transaction(self) -> CursorFixedCtxManager:
        return CursorFixedCtxManager(self)


class CursorFixedCtxManager(ContextManager[sqlite3.Cursor]):
    _cursor: sqlite3.Cursor | None = None

    def __init__(self, conn: ConnectionFixedCtxManager):
        self._conn = conn

    def __enter__(self) -> sqlite3.Cursor:
        self._cursor = self._conn.cursor()
        self._cursor.execute("BEGIN")
        return self._cursor

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        value: BaseException | None,
        traceback: TracebackType | None,
    ) -> None:
        assert self._cursor
        if exc_type is None:
            self._conn.commit()
        else:
            self._conn.rollback()
        self._cursor.close()
        self._cursor = None

Usage:

db = sqlite3.connect(..., isolation_level=None, factory=ConnectionFixedCtxManager)

with db.transaction() as cursor:
    cursor.execute("insert into foo values (1);")

Pretty simiilar to the .savepoint() suggestion by @erlend-aasland above except I think the context manager should return a cursor to prevent mixing up the main db object with the cursor. My code doesn't do anything for nested transactions since I don't use those. The separation between connection and cursor is still not really clean, IMO all convenience methods like db.execute() should throw an error when .transaction() was called / in_transaction == True

Edit: I see there's some efforts to maybe fix this soon. Awesome!

erlend-aasland · 2022-07-15T11:48:17Z

The separation between connection and cursor is still not really clean, IMO all convenience methods like db.execute() should throw an error when .transaction() was called / in_transaction == True

That would probably break existing code, so that is not an option.

The docs have been made more explicit in the last weeks. Hopefully that will reduce the confusion. Also, the upcoming autocommit attribute will introduce a cleaner API that should be easier to understand, imo.

phiresky · 2022-07-15T11:52:09Z

It wouldn't be a breaking change if it only happens with a new .savepoint() / .transaction() method right? My idea would be that while the context manager created from that function is open, the main Connection object would basically be disabled and not usable.

Otherwise the __enter__ method should probably return None and not Connection (as the current contextmanager does) or Cursor (as my suggestion). If it returns something I'd expect what it returns to be different and statements on the main connection object to be unaffected

erlend-aasland · 2022-07-15T12:21:09Z

Let's move this discussion to either Discourse or a new issue.

bitdancer added easy extension-modules C modules in the Modules dir stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Jan 14, 2013

ghaering mannequin self-assigned this Jan 11, 2015

vstinner removed the easy label Aug 13, 2019

ezio-melotti transferred this issue from another repository Apr 10, 2022

erlend-aasland added the topic-sqlite3 label May 16, 2022

erlend-aasland mentioned this issue Jun 14, 2022

Add an autocommit property to sqlite3.Connection with a PEP 249 compliant manual commit mode and migrate #83638

Closed

mwichmann mentioned this issue Jun 16, 2022

gh-61162: Clarify sqlite3 connection context manager docs #93890

Merged

erlend-aasland closed this as completed Jun 19, 2022

erlend-aasland mentioned this issue Jul 27, 2022

Improve the sqlite3 reference #95273

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The sqlite3 context manager does not work with isolation_level=None #61162

The sqlite3 context manager does not work with isolation_level=None #61162

bitdancer commented Jan 14, 2013

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ghaering mannequin commented Aug 19, 2015

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Kodiologist mannequin commented Mar 25, 2022

erlend-aasland commented Jun 16, 2022 •

edited

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phiresky commented Jul 15, 2022 •

edited

erlend-aasland commented Jul 15, 2022

phiresky commented Jul 15, 2022 •

edited

erlend-aasland commented Jul 15, 2022

The sqlite3 context manager does not work with isolation_level=None #61162

The sqlite3 context manager does not work with isolation_level=None #61162

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bitdancer commented Jan 14, 2013

bitdancer commented Jan 14, 2013

loewis mannequin commented Jan 14, 2013

bitdancer commented Jan 14, 2013

aymericaugustin mannequin commented Jun 6, 2014

ghaering mannequin commented Aug 19, 2015

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erlend-aasland commented Jun 16, 2022 • edited

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