use "as" for block scope support

[lyricconch]

BPO	12635
Nosy	@ezio-melotti

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2011-07-25.09:02:47.766>
created_at = <Date 2011-07-25.07:36:47.154>
labels = ['interpreter-core', 'type-feature']
title = 'use "as" for block scope support'
updated_at = <Date 2011-07-25.09:02:47.765>
user = 'https://bugs.python.org/lyricconch'

bugs.python.org fields:

activity = <Date 2011-07-25.09:02:47.765>
actor = 'ezio.melotti'
assignee = 'none'
closed = True
closed_date = <Date 2011-07-25.09:02:47.766>
closer = 'ezio.melotti'
components = ['Interpreter Core']
creation = <Date 2011-07-25.07:36:47.154>
creator = 'lyricconch'
dependencies = []
files = []
hgrepos = []
issue_num = 12635
keywords = []
message_count = 2.0
messages = ['141076', '141077']
nosy_count = 2.0
nosy_names = ['ezio.melotti', 'lyricconch']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue12635'
versions = []

[lyricconch]

use "as" for block scope support
just like mozilla javascript "let" extension
https://developer.mozilla.org/en/new_in_javascript_1.7#Block_scope_with_let_%28Merge_into_let_Statement%29

usage:

as_clause(as_declare): "as" NAME
as_stmt: NAME "as" test
as_expr: "(" expr "as" NAME ")" expr

var declare by as_clause is alive in <suite> only
eg:
<NAME "f" binding saved>with open(...) as f<NAME "f" bind to HEAPObj>:
...
<NAME "f" binding restored>

the same rule to "except E as e: "

spec:
from socket import AF_INET as IPv4
<IPv4 bind to socket.AF_INET slot>
IPv4 = None
assert socket.AF_INET == None

var in as_stmt is alive in current indentation
eg:
for i in range(10):
<NAME "t" binding saved>
t as f()+1 <NAME "t" bind to f()+1>
...
<NAME "t" binding restored>

var in as_expr is alive in sub expr only
eg:
t = None
x = (2+3 as t) t**2
assert t == None ane x == 25

Suggestion:
new opcode
ENTER_BLOCK #depth #varslots

[ezio-melotti]

You should propose this to the python-ideas mailing list first.
It might be worth checking the archives of the ML as well -- I think I saw already something similar a while ago.