Expose `capture_locals` parameter in `traceback` convenience functions

[ulope]

BPO	33809
Nosy	@bitdancer, @farhaanbukhsh, @iritkatriel
PRs	bpo-33809: add the TracebackException.print() method #24231

^{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 = <Date 2021-05-22.16:41:50.866>
created_at = <Date 2018-06-08.15:52:20.399>
labels = ['type-feature', 'library', '3.11']
title = 'Expose `capture_locals` parameter in `traceback` convenience functions'
updated_at = <Date 2021-09-16.18:04:41.193>
user = 'https://bugs.python.org/ulope'

bugs.python.org fields:

activity = <Date 2021-09-16.18:04:41.193>
actor = 'iritkatriel'
assignee = 'none'
closed = True
closed_date = <Date 2021-05-22.16:41:50.866>
closer = 'iritkatriel'
components = ['Library (Lib)']
creation = <Date 2018-06-08.15:52:20.399>
creator = 'ulope'
dependencies = []
files = []
hgrepos = []
issue_num = 33809
keywords = ['patch']
message_count = 14.0
messages = ['319079', '319809', '320176', '320191', '385028', '385029', '385030', '385055', '385056', '385089', '385106', '385108', '401975', '401976']
nosy_count = 4.0
nosy_names = ['r.david.murray', 'ulope', 'fhackdroid', 'iritkatriel']
pr_nums = ['24231']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue33809'
versions = ['Python 3.11']

[ulope]

Since 3.5 the internal machinery of the traceback module has gained the very useful ability to capture locals.

It would be useful to also expose that ability through the various convenience functions.

[farhaanbukhsh]

Hey, I would like to work on this, where do I start or how can I help?

[bitdancer]

I think we should get one or more of the core devs who were involved in the changes that added that parameter to sign off on whether this is a good idea or not (I have no opinion at the moment). You should be able to find them via git blame and looking at the issues related to the changesets you find. Unless someone who remembers comes along and just adds them to nosy :)

[farhaanbukhsh]

Hahah! Let me try to put this on the IRC channel may be someone can help us there.

[iritkatriel]

I don't understand this request. If you ask TracebackExceptions to capture_locals then the FrameSummary object gets a dict of the reprs of the locals, which can be introspected and participate in __eq__ checks but nothing else happens with them. What would the convenience functions do with this parameter?

Ulrich, can you explain the use case or how you see this working?

[iritkatriel]

Sorry, I spoke too soon - see now that the locals are use in the StackSummary.format().

[iritkatriel]

That said, you can always use

TracebackException.from_exception(exc, capture_locals=True).format()

which is not much longer than

print_exception(exc, capture_locals=True)

[ulope]

Functionally equivalent code would be:

print("".join(TracebackException.from_exception(ex, capture_locals=True).format()))

vs. (hypothetically)

print_exc(capture_locals=True)

Which is quite a significant difference IMO.

[iritkatriel]

I’m not sure I agree that it’s a big win.
You can always add such a utility function in your code.

[iritkatriel]

On the other hand, I think it makes sense to add a print() method to TracebackException so that you can do

TracebackException.from_exception(ex, capture_locals=True).print(file)

or whatever other combination of current or future params.