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Tokenize module does not mirror "end-of-input" is newline behavior #78080
Description
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 = 'https://github.com/ammaraskar'
closed_at = <Date 2018-07-06.10:24:50.699>
created_at = <Date 2018-06-19.07:41:52.217>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'Tokenize module does not mirror "end-of-input" is newline behavior'
updated_at = <Date 2019-03-22.11:46:47.154>
user = 'https://github.com/ammaraskar'bugs.python.org fields:
activity = <Date 2019-03-22.11:46:47.154>
actor = 'brechtm'
assignee = 'ammar2'
closed = True
closed_date = <Date 2018-07-06.10:24:50.699>
closer = 'taleinat'
components = ['Library (Lib)']
creation = <Date 2018-06-19.07:41:52.217>
creator = 'ammar2'
dependencies = []
files = []
hgrepos = []
issue_num = 33899
keywords = ['patch']
message_count = 27.0
messages = ['319934', '321154', '321162', '321163', '321164', '321165', '328220', '328222', '328226', '328227', '328238', '328283', '328318', '328324', '328353', '328354', '328355', '328356', '328357', '328358', '328359', '328360', '328369', '328383', '328877', '330213', '338601']
nosy_count = 11.0
nosy_names = ['terry.reedy', 'gregory.p.smith', 'taleinat', 'benjamin.peterson', 'ned.deily', 'meador.inge', 'brechtm', 'Anthony Sottile', 'ammar2', 'miss-islington', 'asmeurer']
pr_nums = ['7891', '8132', '8133', '8134', '10072', '10073', '10074', '10075']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33899'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']
Activity
ammaraskar commentedon Jun 19, 2018
As was pointed out in https://bugs.python.org/issue33766 there is an edge case in the tokenizer whereby it will implicitly treat the end of input as a newline. The tokenize module in stdlib does not mirror the C code's behavior in this case.
tokenizer.c:
~/cpython $ echo -n 'x' | ./python
----------
NAME ("x")
NEWLINE
ENDMARKER
tokenize module:
~/cpython $ echo -n 'x' | ./python -m tokenize
1,0-1,1: NAME 'x'
2,0-2,0: ENDMARKER ''
The instrumentation to have the C tokenizer dump out its tokens is mine, can provide a diff to produce that output if needed.
taleinat commentedon Jul 6, 2018
New changeset c4ef489 by Tal Einat (Ammar Askar) in branch 'master':
bpo-33899: Make tokenize module mirror end-of-file is end-of-line behavior (GH-7891)
c4ef489
taleinat commentedon Jul 6, 2018
New changeset ab75d9e by Tal Einat (Ammar Askar) in branch '3.7':
[3.7] bpo-33899: Make tokenize module mirror end-of-file is end-of-line behavior (GH-7891) (GH-8132)
ab75d9e
taleinat commentedon Jul 6, 2018
New changeset 11c36a3 by Tal Einat (Ammar Askar) in branch '3.6':
[3.6] bpo-33899: Make tokenize module mirror end-of-file is end-of-line behavior (GH-7891) (GH-8134)
11c36a3
taleinat commentedon Jul 6, 2018
New changeset 7829bba by Tal Einat (Ammar Askar) in branch '2.7':
[2.7] bpo-33899: Make tokenize module mirror end-of-file is end-of-line behavior (GH-7891) (bpo-8133)
7829bba
taleinat commentedon Jul 6, 2018
Thanks for all of your work on this, Ammar!
asottile commentedon Oct 21, 2018
This change in behaviour is breaking pycodestyle: PyCQA/pycodestyle#786
Perhaps it shouldn't have been backported (especially all the way to python2.7?)
taleinat commentedon Oct 21, 2018
This was backported since it was considered a bug, but you are right that it broke backwards compatibility, and perhaps shouldn't have been backported.
Still, with 3.6.6 and 3.7.1 now released, that ship has sailed.
We could perhaps revert this on the 2.7 branch, but I feel that reverting this change only on 2.7 would just cause even more confusion.
asottile commentedon Oct 21, 2018
I'm surprised this was classified as a bug! Though that's subjective so I get that it's difficult to decide what is and what isn't ¯\(ツ)/¯
4 remaining items
benjaminp commentedon Oct 23, 2018
Please revert in 2.7.
taleinat commentedon Oct 24, 2018
See PR #54281 for reverting in 2.7.
gpshead commentedon Oct 24, 2018
FYI, An example of other fallout from this change - patsy broke and needed this fix:
pydata/patsy@4f53bba#diff-53c70e68c6dfd4fe9b08427792cb2bd6
taleinat commentedon Oct 24, 2018
See PR #54282 adding mention in "What's New".
gpshead commentedon Oct 24, 2018
some pylint fallout appears to be addressed in pylint-dev/pylint@2698cbe
gpshead commentedon Oct 24, 2018
New changeset dfba1f6 by Gregory P. Smith (Tal Einat) in branch 'master':
bpo-33899: Mention tokenize behavior change in What's New (GH-10073)
dfba1f6
miss-islington commentedon Oct 24, 2018
New changeset 9a04762 by Miss Islington (bot) (Tal Einat) in branch '3.6':
[3.6] bpo-33899: Mention tokenize behavior change in What's New (GH-10073) (GH-10075)
9a04762
miss-islington commentedon Oct 24, 2018
New changeset b4c9874 by Miss Islington (bot) (Tal Einat) in branch '3.7':
[3.7] bpo-33899: Mention tokenize behavior change in What's New (GH-10073) (GH-10074)
b4c9874
taleinat commentedon Oct 24, 2018
Thanks for helping with the fallout from this, Gregory.
terryjreedy commentedon Oct 24, 2018
bpo-33766 was about documenting the C tokenizer change, some years ago, that made end-of-file EOF and end-of-string EOS generate the NEWLINE token required to properly terminate statements. "The end of input also serves
as an implicit terminator for the final physical line."
Although the tokenizer module intentionally does not exactly mirror the C tokenizer (it adds COMMENT tokens), it plausibly seems like a bug that it was not changed along with the C tokenizer, as it has since been tokenizing valid code as grammatically invalid. But I agree that this fix is too disruptive for 2.7.
benjaminp commentedon Oct 24, 2018
New changeset a1f45ec by Benjamin Peterson (Tal Einat) in branch '2.7':
bpo-33899: Revert tokenize module adding an implicit final NEWLINE (GH-10072)
a1f45ec
gpshead commentedon Oct 29, 2018
https://bugs.python.org/issue35107 filed to track further fallout from this API change.
asmeurer commentedon Nov 21, 2018
Is it expected behavior that comments produce NEWLINE if they don't have a newline and don't produce NEWLINE if they do (that is, '# comment' produces NEWLINE but '# comment\n' does not)?
brechtm commentedon Mar 22, 2019
In order to adapt code to this change, can we assume that a NEWLINE token with an empty string only occurs right before the ENDMARKER?