Include column offsets for bytecode instructions

@terryjreedy

BPO	43950
Nosy	@terryjreedy, @nedbat, @aroberge, @markshannon, @serhiy-storchaka, @ammaraskar, @pablogsal, @miss-islington, @brandtbucher, @isidentical, @sweeneyde, @sobolevn
PRs	bpo-43950: Initial base implementation for PEP 657 #26955 bpo-43950: Print columns in tracebacks (PEP 657) #26958 bpo-43950: optimize column table assembling with pre-sizing the column table #26997 bpo-43950: use 0-indexed column offsets for bytecode positions #27011 bpo-43950: include position in dis.Instruction #27015 bpo-43950: Add option to opt-out of PEP-657 #27023 bpo-43950: Add option to opt-out of PEP-657 #27023 bpo-43950: Add option to opt-out of PEP-657 #27023 bpo-43950: Specialize tracebacks for subscripts/binary ops #27037 bpo-43950: Add documentation for PEP-657 #27047 bpo-43950: implement on-the-fly source tracking for interactive mode #27117 bpo-43950: make BinOp specializations more reliable #27126 bpo-43950: distinguish errors happening on character offset decoding #27217 bpo-43950: ensure source_line is present when specializing the traceback #27313 bpo-43950: support long lines in traceback.py #27336 bpo-43950: check against the raw string, not the pyobject #27337 bpo-43950: support some multi-line expressions for PEP 657 #27339 bpo-43950: support positions for dis.Instructions created through dis.Bytecode #28142 bpo-43950: handle wide unicode characters in tracebacks #28150

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

Show more details

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-04-27.10:58:38.225>
labels = []
title = 'Include column offsets for bytecode instructions'
updated_at = <Date 2022-01-18.12:31:06.245>
user = 'https://github.com/pablogsal'

bugs.python.org fields:

activity = <Date 2022-01-18.12:31:06.245>
actor = 'sobolevn'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-04-27.10:58:38.225>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 43950
keywords = ['patch']
message_count = 39.0
messages = ['392054', '392062', '392081', '392082', '392520', '392540', '392541', '392555', '392557', '396866', '396874', '396950', '396957', '396962', '397109', '397352', '397368', '397589', '397666', '397667', '397669', '397673', '397829', '397837', '397844', '397882', '397909', '397910', '397911', '397914', '397915', '398089', '398144', '398169', '398170', '398172', '398197', '400998', '410856']
nosy_count = 12.0
nosy_names = ['terry.reedy', 'nedbat', 'aroberge', 'Mark.Shannon', 'serhiy.storchaka', 'ammar2', 'pablogsal', 'miss-islington', 'brandtbucher', 'BTaskaya', 'Dennis Sweeney', 'sobolevn']
pr_nums = ['26955', '26958', '26997', '27011', '27015', '27023', '27023', '27023', '27037', '27047', '27117', '27126', '27217', '27313', '27336', '27337', '27339', '28142', '28150']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue43950'
versions = []

If we could include column offsets from the AST nodes for every bytecode instructions we could leverage these to offer much better tracebacks and a lot more information to debuggers and similar tools. For instance, in an expression such as:

z['aaaaaa']['bbbbbb']['cccccc']['dddddd].sddfsdf.sdfsdf

where one of these elements is None, we could tell exactly what of these pieces is the actual None and we could do some cool highlighting on tracebacks.

Similarly, coverage tools and debuggers could also make this distinction and therefore could offer reports with more granularity.

The cost is not 0: it would be two integers per bytecode instruction, but I think it may be worth the effort.

I'm going to prepare a PEP since the discussion regarding if the two integers per bytecode are worth enough is going to be eternal.

The additional cost will not only be the line number table, but we need to store the line for exceptions that are reraised after cleanup.
Adding a column will mean more stack consumption.

Yup, but I still think is worth the cost, giving that debugging improvements are usually extremely popular among users.

Specific examples of current messages and proposed improvements would help focus discussion.

If you are willing to only handle code lines up to 256 chars, only 2 bytes should be needed. (0,0) or (255,255) could mean 'somewhere beyond the 256th char'.

Specific examples of current messages and proposed improvements would help focus discussion.

Yeah, I am proposing going from:

>>> x['aaaaaa']['bbbbbb']['cccccc']['dddddd'].sddfsdf.sdfsdf
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not subscriptable

to

>>> x['aaaaaa']['bbbbbb']['cccccc']['dddddd'].sddfsdf.sdfsdf
                         ^^^^^^^^^^
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not subscriptable

Basically, to highlight in all exceptions the range in the displayed line where the error ocurred. For instance:

>>> foo(a, b/z+2, c, 132432 /x, d /y)
                     ^^^^^^^^^
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero

Marking what expression evaluated to None would be extremely helpful. So would marking the 0 denominator when there is more than one candidate: "e = a/b + c/d". It should be easy to revise IDLE Shell's print_exception to tag the span. In some cases, the code that goes from a traceback line to a line in a file and marks it could do the same.

What would you do when the expression is not the last line?

try:
x/y
...
except Exception as e:
...
raise e

The except and raise might even be in a separate module.
I look forward to the PEP and discussion.

So would marking the 0 denominator when there is more than one candidate: "e = a/b + c/d".

No, it will mark the offset of the bytecode that was getting executed when the exception was raised. Is just a way to mark what is raising the particular exception

What would you do when the expression is not the last line?

There is some logic needed to re-raise exceptions. But basically it boils down to comparate the line numbers to decide if you want to propagate or not the offsets.

New changeset 98eee94 by Pablo Galindo in branch 'main':
bpo-43950: Add code.co_positions (PEP-657) (GH-26955)
98eee94

New changeset ec8759b by Batuhan Taskaya in branch 'main':
bpo-43950: optimize column table assembling with pre-sizing object (GH-26997)
ec8759b

New changeset 44f91fc by Batuhan Taskaya in branch 'main':
bpo-43950: use 0-indexed column offsets for bytecode positions (GH-27011)
44f91fc

New changeset 693cec0 by Batuhan Taskaya in branch 'main':
bpo-43950: include position in dis.Instruction (GH-27015)
693cec0

New changeset 5644c7b by Ammar Askar in branch 'main':
bpo-43950: Print columns in tracebacks (PEP-657) (GH-26958)
5644c7b

New changeset 4823d9a by Ammar Askar in branch 'main':
bpo-43950: Add option to opt-out of PEP-657 (GH-27023)
4823d9a

As awkward of a beast as a tuple subclass emulating the previous fixed size namedtuple while adding additional attributes seems, it is very practical.

Users don't care about the specifics. They just need existing code to keep working and will want access to new values when updating this code or writing new code. Which means it should still be a tuple subclass for typing reasons known as inspect.Traceback and inspect.FrameInfo, support the existing indices and unpacking semantics, and support named field access. That this would be adding additional fields that indexing does not provide is a mere curiosity that most users would not notice as modern code should be field based anyways.

Nobody should care if the implementation behind the returned instances is unusual. The behavior will be what they expect. It avoids the need to expand into multiple different return types via an arg flag or the creation of parallel APIs.

This is a good practical example of why we should not design APIs to return tuples if they could conceivably change in the future. And why people unpacking on API calls that return tuples might find it wise to always [:slice] the return value as a style idiom.

All this said... we could also just add another field to the namedtuple. Some code inspection among existing API users is required, but I expect most users either immediately unpack upon return value assignment or use field names. Mix and matching of indexing and named access on a single return value is probably rare. The easy modification to existing code using unpacking to deal with this kind of API change upon version upgrade is to append a [:5] or similar to the API call. We have had other tuple returning APIs add fields in the past where this was the workaround though I've forgotten what they were off the top of my head.

This would be the more disruptive option. It is nice to avoid this if possible as it delays people's ability to update to and even test their code on 3.11. So I still lean towards the hybrid "half namedtuple" class.

GH-88116: Use a compact format to represent end line and column offse…

GH-88116: Document that PyCodeNew is dangerous, and make PyCode_NewEm…

gh-88116: Enhance the inspect frame APIs to use the extended position…

pythongh-88116: Avoid undefined behavior when decoding varints in cod…

gh-88116: Avoid undefined behavior when decoding varints in code obje…

pythongh-88116: Avoid undefined behavior when decoding varints in cod…

gh-88116: Avoid undefined behavior when decoding varints in code obje…

@markshannon

@markshannon I'm noticing that the implementation for varints and signed varints that we use has two encodings for 0 (both uval==0 and uval==1 decode to 0), and no way to encode -2**31. Is this a problem? What prevents us to need to encode -2**31?

@markshannon

Also, weirdly there are two ways to encode 0 and no ways to encode -INT_MIN. @markshannon is this expected?

pythongh-88116: Avoid undefined behavior when decoding varints in cod…

pythongh-88116: Initial work on wide unicode characters

pythongh-88116: Handle wide unicode characters in tracebacks

Navigation Menu

Repository navigation

Include column offsets for bytecode instructions #88116

35 remaining items

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Include column offsets for bytecode instructions #88116

Description

Activity

pablogsal commented on Apr 27, 2021

pablogsal commented on Apr 27, 2021

markshannon commented on Apr 27, 2021

pablogsal commented on Apr 27, 2021

terryjreedy commented on Apr 30, 2021

pablogsal commented on Apr 30, 2021

pablogsal commented on Apr 30, 2021

terryjreedy commented on May 1, 2021

pablogsal commented on May 1, 2021

pablogsal commented on Jul 2, 2021

miss-islington commented on Jul 2, 2021

miss-islington commented on Jul 4, 2021

miss-islington commented on Jul 4, 2021

pablogsal commented on Jul 4, 2021

pablogsal commented on Jul 7, 2021

35 remaining items

gpshead commented on Apr 17, 2022

pablogsal commented on Jun 28, 2022

pablogsal commented on Jun 28, 2022

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions