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add shorthand global and nonlocal statements #48449
Description
| BPO | 4199 |
|---|---|
| Nosy | @akuchling, @birkenfeld, @rhettinger, @gpshead, @amauryfa, @benjaminp, @bitdancer, @ericsnowcurrently |
| Files |
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 2013-06-30.14:12:36.980>
created_at = <Date 2008-10-24.22:32:14.485>
labels = ['interpreter-core', 'type-feature']
title = 'add shorthand global and nonlocal statements'
updated_at = <Date 2013-06-30.14:12:36.945>
user = 'https://github.com/benjaminp'bugs.python.org fields:
activity = <Date 2013-06-30.14:12:36.945>
actor = 'gregory.p.smith'
assignee = 'none'
closed = True
closed_date = <Date 2013-06-30.14:12:36.980>
closer = 'gregory.p.smith'
components = ['Interpreter Core']
creation = <Date 2008-10-24.22:32:14.485>
creator = 'benjamin.peterson'
dependencies = []
files = ['11884', '12254']
hgrepos = []
issue_num = 4199
keywords = ['patch', 'needs review']
message_count = 20.0
messages = ['75193', '77089', '77134', '77159', '88874', '99705', '99958', '99965', '99966', '99977', '99978', '100015', '100043', '100188', '110694', '110698', '155723', '155865', '192049', '192070']
nosy_count = 10.0
nosy_names = ['jhylton', 'akuchling', 'georg.brandl', 'rhettinger', 'gregory.p.smith', 'amaury.forgeotdarc', 'benjamin.peterson', 'r.david.murray', 'BreamoreBoy', 'eric.snow']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'patch review'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue4199'
versions = ['Python 3.4']
Activity
benjaminp commentedon Oct 24, 2008
PEP-3104 says that the nonlocal and global statements should allow a
shorthand. ("global x; x = 3" == "global x = 3") This patch implements that.
benjaminp commentedon Dec 6, 2008
Please review.
amauryfa commentedon Dec 6, 2008
the add_ast_fields() function seems to be added by this patch, but it
is already in svn.
Are 1-tuple supported?
benjaminp commentedon Dec 6, 2008
I think I may have been merging add_ast_fields when I wrote the patch.
Here's a new patch that handles "global x, = (5,)". To do it, I added a
new flag* to the Global and Nonlocal AST objects that indicates whether
the value needs to be unpacked or not.
birkenfeld commentedon Jun 4, 2009
Postponed to 3.2.
akuchling commentedon Feb 22, 2010
Bumping priority so this doesn't get forgotten before 3.2; it seems important because it fixes noncompliance with a PEP.
birkenfeld commentedon Feb 23, 2010
"High" is not high enough :)
jhylton commentedon Feb 23, 2010
Is deferred blocker a higher priority?
Jeremy
On Tue, Feb 23, 2010 at 4:37 PM, Georg Brandl <report@bugs.python.org> wrote:
birkenfeld commentedon Feb 23, 2010
I interpret the "Priority" list view contents to be sorted by priority, so "deferred blocker" is the second-highest.
jhylton commentedon Feb 23, 2010
On Sat, Dec 6, 2008 at 1:28 PM, Benjamin Peterson
<report@bugs.python.org> wrote:
You shouldn't need to do this. The unpack is implied if the number of
identifiers is greater than 1.
Jeremy
jhylton commentedon Feb 23, 2010
I also notice that the Grammar in the PEP is more complicated:
nonlocal_stmt ::=
"nonlocal" identifier ("," identifier)*
["=" (target_list "=")+ expression_list]
| "nonlocal" identifier augop expression_list
The Grammar in the patch is:
+global_stmt: 'global' NAME (',' NAME)* [','] ['=' testlist]
+nonlocal_stmt: 'nonlocal' NAME (',' NAME)* [','] ['=' testlist]
It appears that the PEP is trying to support:
nonlocal x = y = z = 1
nonlocal a, b = c, d = 1
If we're going to support the PEP as written, I think we need to
modify Global() and Nonlocal() to look exactly like Assign(), but add
an extra check to verify that all of the expressions in the targets
are Name, List, or Tuple. You'd probably want to check this at the
time you are generating the AST, so that you're not stuck with some
extra state in the compiler traversal about whether you are generating
code for a Global() or an Assign().
This approach makes the compiler code very simple. We use exactly the
same code for Global(), Nonlocal(), and Assign(). It does have the
downside that you need to enforce this unwritten constraint of the AST
in ast.c and in the ast module.
It also means that the AST will change in a non-backwards compatible
way. I don't see how to do that given that we're also changing the
language spec. (Do you want to include the spec change in your
patch?)
Jeremy
On Tue, Feb 23, 2010 at 6:41 PM, Jeremy Hylton <jeremy@alum.mit.edu> wrote:
birkenfeld commentedon Feb 24, 2010
It also tries to support augmented assignment; however I'm not sure what the semantics of that should be.
Further, there is an ambiguity if too much freedom is allowed: what about
global x = 1, y
Is it declaring a global "x" and assigning a tuple, or declaring a global "x" and a global "y"?
I would not support List or Tuple as targets. Same basic problem as
above, and I don't see a use case.
I see two possibilities for the actual syntax:
global *either* supports multiple identifiers, *or* one identifier
and an assignment.
global always supports multiple identifiers, each with an optional
assignment; tuples need parentheses.
In both cases, I would keep it simple and not allow multiple targets or
augmented assignment.
jhylton commentedon Feb 24, 2010
I guess there's some question about whether the syntax in the PEP was
considered carefully when it was approved. If so, I'm not sure that
we want to re-open the discussion. On the other hand, it's been a
long time since the PEP was approved and we do have a moratorium on
language changes, so it doesn't hurt to slow things down.
I'd argue that the intent of the PEP is pretty clear. You can take
any assignment statement where the LHS doesn't have subscripts, put a
nonlocal or global in front of it, and it means that all those
assignments are to global/nonlocal variables.
Jeremy
On Wed, Feb 24, 2010 at 4:20 AM, Georg Brandl <report@bugs.python.org> wrote:
birkenfeld commentedon Feb 27, 2010
I do think a brief discussion after the moratorium is over would be good.
BreamoreBoy commentedon Jul 18, 2010
I'm not sure as to the status of this. Could it go back to (say) 3.3, is it still a candidate for 3.2(.x), or what?
benjaminp commentedon Jul 18, 2010
2010/7/18 Mark Lawrence <report@bugs.python.org>:
It can't do anything until 3.3.
bitdancer commentedon Mar 14, 2012
We could also just decide we don't need it :)
If we do (I haven't read the PEP) does a statement with an assignment make the variable global in that scope, or does it only affect the global variable for the duration of the assignment, and otherwise the variable remains local in the scope? (I don't know which to guess, and the ambiguity is disturbing. I like the current clarity even if it is more typing.)
rhettinger commentedon Mar 15, 2012
+1 on the feature as described in the PEP.
akuchling commentedon Jun 29, 2013
Bumping version to 3.4. I'll send a note to python-dev about this issue.
gpshead commentedon Jun 30, 2013
Closing and rejecting based on said discussion. http://mail.python.org/pipermail/python-dev/2013-June/127143.html