unpack list of singleton tuples not unpacking

[atuining]

BPO	1520864
Nosy	@birkenfeld, @rhettinger
Files	lc-tuple-fix.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 2006-09-05.04:01:08.000>
created_at = <Date 2006-07-11.23:21:13.000>
labels = ['interpreter-core']
title = 'unpack list of singleton tuples not unpacking'
updated_at = <Date 2006-09-05.04:01:08.000>
user = 'https://bugs.python.org/atuining'

bugs.python.org fields:

activity = <Date 2006-09-05.04:01:08.000>
actor = 'nnorwitz'
assignee = 'nnorwitz'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2006-07-11.23:21:13.000>
creator = 'atuining'
dependencies = []
files = ['2065']
hgrepos = []
issue_num = 1520864
keywords = []
message_count = 6.0
messages = ['29136', '29137', '29138', '29139', '29140', '29141']
nosy_count = 5.0
nosy_names = ['nnorwitz', 'georg.brandl', 'rhettinger', 'atuining', 'sadrejeb']
pr_nums = []
priority = 'critical'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1520864'
versions = ['Python 2.5']

[atuining]

The following code works differently in Python 2.5 than
Python 2.4:

x = [(1,), (2,), (3,)]
for y, in x:
    print y

In Python 2.4, this code produces the following:
1
2
3

In Python 2.5, this code produces the following:
(1,)
(2,)
(3,)

Interestingly enough the following code:

x = (1,)
y, = x
print y

produces the output
1

in both Python 2.4 and Python 2.5. I'm thinking this is
not intentional. :-)

[rhettinger]

Logged In: YES
user_id=80475

Ouch. This is bad. The disassembly shows that the compiler
isn't generating the unpack_sequence opcode.

[nnorwitz]

Logged In: YES
user_id=33168

Awww come on, can't we change the language just to make your
life difficult? ;-)

Thanks a lot for catching this!

Committed revision 50597.

[sadrejeb]

Logged In: YES
user_id=26911

I have the impression that the bug has only been partially
solved, i.e. in 2.5c1, singleton tuples don't get unfoled in
list comprehensions.

Python 2.5c1 (r25c1:51305, Sep  4 2006, 10:15:09)
[GCC 4.1.1 20060525 (Red Hat 4.1.1-1)] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
>>> l = [(1,), (2,)]
>>> print [x for x, in l]
[(1,), (2,)]

Same example in Python 2.4.3:

Python 2.4.3 (#1, Jul 25 2006, 11:53:03)
[GCC 4.1.1 20060525 (Red Hat 4.1.1-1)] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
>>> l = [(1,), (2,)]
>>> print [x for x, in l]
[1, 2]

[birkenfeld]

Logged In: YES
user_id=849994

You're right. Attached patch fixes this.

[nnorwitz]

Logged In: YES
user_id=33168

Thanks for spotting this. Let us know if you find any more
bugs.

Well, I'm glad Georg and I came up with the same basic patch
(thanks Georg!). I had worked it up prior to seeing his
version here. It's also the same fix for the for loops.

Committed revision 51729. (2.6)
Committed revision 51730. (2.5)