ast.literal_eval fails on sets

[alex]

BPO	13536
Nosy	@brettcannon, @birkenfeld, @ncoghlan, @benjaminp, @alex, @briancurtin
Superseder	bpo-10091: ast.literal_eval does not handled new set literals
Files	x.diff

^{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 2011-12-06.01:47:59.785>
created_at = <Date 2011-12-06.01:02:39.729>
labels = ['invalid']
title = 'ast.literal_eval fails on sets'
updated_at = <Date 2011-12-06.11:51:13.603>
user = 'https://github.com/alex'

bugs.python.org fields:

activity = <Date 2011-12-06.11:51:13.603>
actor = 'georg.brandl'
assignee = 'none'
closed = True
closed_date = <Date 2011-12-06.01:47:59.785>
closer = 'benjamin.peterson'
components = []
creation = <Date 2011-12-06.01:02:39.729>
creator = 'alex'
dependencies = []
files = ['23859']
hgrepos = []
issue_num = 13536
keywords = ['patch']
message_count = 6.0
messages = ['148897', '148898', '148899', '148900', '148901', '148910']
nosy_count = 6.0
nosy_names = ['brett.cannon', 'georg.brandl', 'ncoghlan', 'benjamin.peterson', 'alex', 'brian.curtin']
pr_nums = []
priority = 'low'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = '10091'
type = None
url = 'https://bugs.python.org/issue13536'
versions = ['Python 2.7']

[alex]

In 2.7 ast.literal_eval blows up with a set for input:

>> import ast
>> ast.literal_eval("{1}")

[alex]

Patch with tests

[briancurtin]

I don't profess to have any special ast knowledge, but given the context around there and the fact that it works...it looks fine to me.

[ncoghlan]

Dict and Set comprehensions are also broken:

>>> {1 for x in ()}
set([])
>>> {1:2 for x in ()}
{}
>>> ast.literal_eval("{1 for x in ()}")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/ast.py", line 80, in literal_eval
    return _convert(node_or_string)
  File "/usr/lib64/python2.7/ast.py", line 79, in _convert
    raise ValueError('malformed string')
ValueError: malformed string
>>> ast.literal_eval("{1:2 for x in ()}")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/ast.py", line 80, in literal_eval
    return _convert(node_or_string)
  File "/usr/lib64/python2.7/ast.py", line 79, in _convert
    raise ValueError('malformed string')
ValueError: malformed string

[alex]

There's no support for comprehensions of any sort, and confusingly limited support for arithmetic ops, I'd like to keep the scope of this issue small, basically backporting 90bf0631bfb8 and adding the tests (which I can also add to default).

[birkenfeld]

Alex: IMO the operator support is only required for complex "literals".