Issue 30682: f-string assert is too restrictive (original) (raw)

This issue has been migrated to GitHub: https://github.com/python/cpython/issues/74867

classification

process

Created on 2017-06-16 09:13 by eric.smith, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Messages (5)
msg296166 - (view)	Author: Eric V. Smith (eric.smith) *	Date: 2017-06-16 09:13
>>> eval("f'\\\n'") python: Python/ast.c:4906: FstringParser_ConcatFstring: Assertion `!state->last_str |	PyUnicode_GET_LENGTH(state->last_str) != 0' failed. [2] 12810 abort (core dumped) ./python The problem is that some literal strings are zero length. The assert can be deleted.
msg296174 - (view)	Author: Serhiy Storchaka (serhiy.storchaka) *	Date: 2017-06-16 10:19
New changeset 11e97f2f80bf65cc828c127eafc95229df35d403 by Serhiy Storchaka (ericvsmith) in branch 'master': bpo-30682: Removed a too-strict assertion that failed for certain f-strings. (#2232) https://github.com/python/cpython/commit/11e97f2f80bf65cc828c127eafc95229df35d403
msg296193 - (view)	Author: Eric V. Smith (eric.smith) *	Date: 2017-06-16 13:29
New changeset 2eca5b465f7404cc8484457b7966f828f434ec20 by ericvsmith (Serhiy Storchaka) in branch '3.6': [3.6] bpo-30682: Removed a too-strict assertion that failed for certain f-strings. (GH-2232) (#2242) https://github.com/python/cpython/commit/2eca5b465f7404cc8484457b7966f828f434ec20
msg296204 - (view)	Author: Terry J. Reedy (terry.reedy) *	Date: 2017-06-16 15:35
Before the patch, eval("f'\\\n'") gives me the same assertion failure, with an IDLE freeze instead of core dump equivalent, but is seems that the string should be of length 2. >>> len('\\\n') 2 >>> len(f'\\\n') 2
msg296212 - (view)	Author: Eric V. Smith (eric.smith) *	Date: 2017-06-16 16:49
Terry: The eval is important. The bug was in evaluating an f-string that consisted of two bytes: a backslash followed by a newline. And just as: eval("'\\\n'") == '' # len == 0 so should eval("f'\\\n'") == '' # len == 0 It's the second one that was throwing the assertion. The parser was seeing these bytes: f 0x66 ' 0x27 \ 0x5c nl 0xa ' 0x27 and behaving badly (to say the least) by asserting. Without the eval, I can't think of a way to have a string consisting of those two bytes, but I assume someone who's trickier than I can come up with a way.