SyntaxError: assignment expression within assert

[jancespivo]

BPO	41417
Nosy	@gvanrossum, @ronaldoussoren, @serhiy-storchaka, @jancespivo
Superseder	bpo-39909: Assignment expression in assert causes SyntaxError

^{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 2020-07-28.10:18:58.773>
created_at = <Date 2020-07-28.07:59:37.953>
labels = ['interpreter-core', 'type-bug', '3.8']
title = 'SyntaxError: assignment expression within assert'
updated_at = <Date 2020-07-28.10:18:58.771>
user = 'https://github.com/jancespivo'

bugs.python.org fields:

activity = <Date 2020-07-28.10:18:58.771>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2020-07-28.10:18:58.773>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2020-07-28.07:59:37.953>
creator = 'jan.cespivo'
dependencies = []
files = []
hgrepos = []
issue_num = 41417
keywords = []
message_count = 4.0
messages = ['374476', '374478', '374479', '374482']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'ronaldoussoren', 'serhiy.storchaka', 'jan.cespivo']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '39909'
type = 'behavior'
url = 'https://bugs.python.org/issue41417'
versions = ['Python 3.8']

[jancespivo]

Hi,

it should be useful if assignment expression works within assertion.

For example (real use-case in tests):

assert r := re.match(r"result is (\d+)", tested_text)
assert int(r.group(1)) == expected_number

I haven't found a mention about assertions in https://www.python.org/dev/peps/pep-0572/ so it isn't technically a bug but it might be omission (?).

Thx!

[ronaldoussoren]

I don't know if this limitation is intentional, but not that you can use an assignment expression when you enclose the expression with parenthesis:

>>> assert (a:=1)
>>> a
1
>>>

[jancespivo]

Hi Ronald,

thank you. It works! :)

[serhiy-storchaka]

It is a duplicate of bpo-39909.