Congrats to Chris for breaking his PEP curse

Abdur-Rahmaan Janhangeer arj.python at gmail.com
Wed Jul 4 00:12:09 EDT 2018


https://www.reddit.com/r/Python/comments/8vmq27/pep_572_assignment_expressions_is_officially/

XD nice feedbacks about the pep

Abdur-Rahmaan Janhangeer
https://github.com/Abdur-rahmaanJ

On Wed, 4 Jul 2018, 06:02 Steven D'Aprano, <
steve+comp.lang.python at pearwood.info> wrote:

> Congratulations to Chris Angelico for breaking the dreaded "any PEP
> written by Chris will be rejected" curse :-)
>
> Guido has announced his intention to accept PEP 572 (assignment
> expressions) once the PEP has been cleaned up a bit.
>
> https://www.python.org/dev/peps/pep-0572/
>
> (The current version of the PEP doesn't quite match the proposal as
> nutted out over about a bazillion emails on two mailing lists starting in
> FEBRUARY!!!)
>
>
> Summary:
>
> Python 3.8 will allow an assignment-as-expression operator. The most
> common uses are expected to be if and while statements:
>
>     condition = expression
>     while condition:
>         do_something()
>         condition = expression
>
> will become:
>
>     while condition := expression:
>         do_something()
>
>
> Cascades of if statements, such as:
>
>     # the dreaded arrowhead anti-pattern
>     mo = re.match(pattern, text)
>     if mo:
>         ...
>     else:
>         mo = re.match(another_pattern, text):
>         if mo:
>             ...
>         else:
>             mo = re.match(third_pattern, text):
>             if mo:
>                 ...
>
>
> will become flatter and easier to read:
>
>     if mo := re.match(pattern, text):
>         ...
>     elif mo := re.match(another_pattern, text):
>         ...
>     elif mo := re.match(third_pattern, text):
>         ...
>
>
> FAQs:
>
> Q. Why Pascal's assignment operator := instead of regular = assignment?
>
> A. To avoid the C bug magnet of mistakenly writing "if x = expr" when
>    you intended to write "if x == expr".
>
>
> Q. Why not use "as"?
>
> A. There is an ambiguity due to with and except statements:
>
>     with expr as name
>
>     except Exception as name
>
>    are already permitted and mean something different to ordinary
>    assignment expressions.
>
>
> Q. Oh no, Python is doomed! This is the end of the world!
>
> A. That's not actually a question, is it?
>
>
>
>
> --
> Steven D'Aprano
> "Ever since I learned about confirmation bias, I've been seeing
> it everywhere." -- Jon Ronson
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>


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