f-strings and string annotations

[serhiy-storchaka]

BPO	33552
Nosy	@ericvsmith, @ambv, @serhiy-storchaka

^{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 2018-05-17.07:03:06.417>
labels = ['interpreter-core', 'type-bug', '3.9', '3.10', '3.11']
title = 'f-strings and string annotations'
updated_at = <Date 2021-10-25.21:44:25.962>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2021-10-25.21:44:25.962>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2018-05-17.07:03:06.417>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 33552
keywords = []
message_count = 1.0
messages = ['316886']
nosy_count = 3.0
nosy_names = ['eric.smith', 'lukasz.langa', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33552'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[serhiy-storchaka]

There are problems with converting annotations containing f-strings into strings (from __future__ import annotations). For example f'''{"'"}''' is converted to f'{"\'"}', but the latter is a syntax error.

>>> from __future__ import annotations
>>> x: f'''{"'"}'''
>>> print(__annotations__['x'])
f'{"\'"}'
>>> x: f'{"\'"}'
  File "<stdin>", line 1
SyntaxError: f-string expression part cannot include a backslash

More complex examples:

f"""{"'''"}"""
f"""{"'" '"'}"""
f"""{"'''"}""" f'''{'"""'}'''

[iritkatriel]

Since 3.12 this fstring is not rejected:

>>> class X:
...   x: f'{"\'"}'
... 
>>> X.__annotations__
{'x': "'"}

>>> from __future__ import annotations
>>> class X:
...   x: f'{"\'"}'
... 
>>> X.__annotations__
{'x': 'f\'{"\\\'"}\''}

[ericvsmith]

I think this can be closed.

[picnixz]

Closing since it now works as intended in 3.12+.