Limit "global" keyword name conflicts in language spec to those enforced by CPython

[ncoghlan]

BPO	14544
Nosy	@rhettinger, @terryjreedy, @ncoghlan, @ezio-melotti, @merwok, @alex

^{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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assignee = None
closed_at = None
created_at = <Date 2012-04-11.04:46:30.833>
labels = ['type-feature']
title = 'Limit "global" keyword name conflicts in language spec to those enforced by CPython'
updated_at = <Date 2015-03-05.10:03:11.434>
user = 'https://github.com/ncoghlan'

bugs.python.org fields:

activity = <Date 2015-03-05.10:03:11.434>
actor = 'ezio.melotti'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2012-04-11.04:46:30.833>
creator = 'ncoghlan'
dependencies = []
files = []
hgrepos = []
issue_num = 14544
keywords = []
message_count = 4.0
messages = ['158005', '158006', '158007', '237252']
nosy_count = 8.0
nosy_names = ['rhettinger', 'terry.reedy', 'ncoghlan', 'fossilet', 'ezio.melotti', 'eric.araujo', 'alex', 'cvrebert']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue14544'
versions = ['Python 3.5']

[ncoghlan]

The language spec currently includes the following paragraph [1]:

Names listed in a global statement must not be defined as
formal parameters or in a for loop control target, class
definition, function definition, or import statement.

While the first restriction is real (and enforced by CPython), since formal parameters are explicitly defined as local variables, there's no obvious rationale for the last 4 restrictions (and CPython doesn't enforce any of them).

The proposal is that the paragraph be simplified to:

Names listed in a global statement must not also be defined as
formal function parameters. Attempting to do so raises SyntaxError.

The current (incorrect!) CPython implementation detail note will be removed.

A similar clarification will also be made in the "nonlocal" statement documentation.

[1] http://docs.python.org/dev/reference/simple_stmts.html#the-global-statement

[alex]

This shouldn't be a problem for PyPy, in fact I'm almost positive that we implement this already (since Django has a test that uses this "feature"). If/when the spec is changed please make sure there are tests for all these cases so we *know* it works though.

[ncoghlan]

Thread link: http://mail.python.org/pipermail/python-ideas/2012-April/014783.html

[rhettinger]

+1 for the proposed change. It should add there is also an enforced (and obvious) restriction that the variable not have been declared nonlocal.