[Python-Dev] PEP 572 and f-strings

[Eric V. Smith]

> On May 12, 2018, at 9:03 AM, Chris Angelico <rosuav at gmail.com> wrote:
> 
>> On Sat, May 12, 2018 at 9:11 PM, Eric V. Smith <eric at trueblade.com> wrote:
>> I don't think it matters to its acceptance, but PEP 572 should at least
>> mention that the := syntax means that you cannot use assignment expressions
>> in f-strings.
>> 
>> As I wrote in a python-ideas email, f'{x:=4}' already has a defined meaning
>> (even if no one is using it).
> 
> As with lambda functions, you can't write them the simple way.
> However, you can parenthesize it, and then it works fine.
> 
>>>> f"@{(lambda: 42)}@"
> '@<function <lambda> at 0x7f09e18c4268>@'
>>>> f"@{(y := 1)}@"
> '@1@'
>>>> y
> 1
> 

Yes, but just as PEP 498 mentions lambdas, I think 572 should mention f-strings, and point out this workaround. 

Eric