[Python-Dev] small Grammar questions

[Andrew Dalke]

Okay, my conclusion is

  def f((a)=5)

is wrong, and the code should be changed to report a better error
message.  I'll file a bug against that.

and I'm going with Brett suggestion that

  [x for x in 1,]

is not supported because it's almost certainly a programming error.  I
think therefore the comment in the Grammar file is distracting.  As
comments can be.


On Feb 20, 2008 3:08 AM, Steve Holden <steve at holdenweb.com> wrote:
> The one that surprised me was the legality of
>
>      def eggs((a, )=c):
>          pass
>
> That just seems like unpacking-abuse to me.

Yep.  Here's another abuse, since I can't figure when someone needs a
destructuring del statement.

>>> class X(object): pass
...
>>> X.a = 123
>>> X.b = "hello"
>>> X.c = 9.801
>>> X.a, X.b, X.c
(123, 'hello', 9.8010000000000002)
>>> del (X.a, (X.b, (X.c,)))
>>> X.a, X.b, X.c
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'X' has no attribute 'a'
>>>

Is this going to be possible in Python3k?

> You really *have* been poking around in little-known crevices, haven't you?

Like this bug from 2.5, fixed in 2.6

>>> from __future__ import with_statement
>>> with f(x=5, 6):
...   pass
...
ValueError: field context_expr is required for With

  :)

        Andrew
        dalke at dalkescientific.com