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From: Oscar Benjamin <oscar.j.benjamin@gmail.com>
Date: Wed, 11 Sep 2013 14:11:22 +0100
Subject: Re: why syntax change in lambda
To: Neal Becker <ndbecker2@gmail.com>
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On 11 September 2013 14:03, Neal Becker <ndbecker2@gmail.com> wrote:
> In py2.7 this was accepted, but not in py3.3.  Is this intentional?  It seems to
> violate the 'principle' that extraneous parentheses are usually allowed/ignored
>
> In [1]: p = lambda x: x
>
> In [2]: p = lambda (x): x
>   File "<ipython-input-2-2b94675a98f1>", line 1
>     p = lambda (x): x
>                ^
> SyntaxError: invalid syntax

I guess it's related to the removal of auto-unpacking of arguments. i.e. in 2.x:

>>> f = lambda (x, y), z: (x, y, z)
>>> f([1, 2], 3)
(1, 2, 3)

However this was removed in 3.x so

>>> f = lambda (x, y), z: (x, y, z)
  File "<stdin>", line 1
    f = lambda (x, y), z: (x, y, z)
               ^
SyntaxError: invalid syntax

Removing that feature would allow a simplification of the lambda
syntax that would have no need to admit any kind of brackets.


Oscar