The string prefixes u and f can't used together

[AifuLIU]

BPO	33551
Nosy	@vstinner, @benjaminp, @ezio-melotti, @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 = <Date 2018-05-17.07:10:00.622>
created_at = <Date 2018-05-17.06:25:08.790>
labels = ['invalid', 'expert-unicode', 'type-crash']
title = "The string prefixes u and f can't used together"
updated_at = <Date 2018-05-17.07:10:00.620>
user = 'https://bugs.python.org/AifuLIU'

bugs.python.org fields:

activity = <Date 2018-05-17.07:10:00.620>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2018-05-17.07:10:00.622>
closer = 'serhiy.storchaka'
components = ['Unicode']
creation = <Date 2018-05-17.06:25:08.790>
creator = 'Aifu LIU'
dependencies = []
files = []
hgrepos = []
issue_num = 33551
keywords = []
message_count = 3.0
messages = ['316883', '316884', '316890']
nosy_count = 5.0
nosy_names = ['vstinner', 'benjamin.peterson', 'ezio.melotti', 'serhiy.storchaka', 'Aifu LIU']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue33551'
versions = ['Python 3.6']

[AifuLIU]

The string prefixes u and f can't used together, for example:

>>> age = 30
>>> s = uf'年龄：{age}'
  File "<stdin>", line 1
    s = uf'年龄：{age}'
                   ^
SyntaxError: invalid syntax
>>>

[benjaminp]

Why would you want to do that?

[serhiy-storchaka]

The string prefix u is used exclusively for compatibility with Python 2. It helps writing code that works in Python 2 and Python 3. The string prefix f is not compatible with Python 2. If you use it, you no longer have reasons for using the string prefix u.