namedtuple should support fully qualified name for more portable pickling

[elibendersky]

BPO	17941
Nosy	@gvanrossum, @warsaw, @rhettinger, @ncoghlan, @ericvsmith, @serhiy-storchaka, @sdrees, @ctismer, @MojoVampire, @ctismer
Files	nt_module.diff: First draft patch to collections

^{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 = 'https://github.com/rhettinger'
closed_at = <Date 2016-09-12.07:19:09.245>
created_at = <Date 2013-05-09.03:46:56.729>
labels = ['type-bug', 'library']
title = 'namedtuple should support fully qualified name for more portable pickling'
updated_at = <Date 2016-09-12.07:19:09.243>
user = 'https://bugs.python.org/elibendersky'

bugs.python.org fields:

activity = <Date 2016-09-12.07:19:09.243>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2016-09-12.07:19:09.245>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2013-05-09.03:46:56.729>
creator = 'eli.bendersky'
dependencies = []
files = ['30243']
hgrepos = ['198']
issue_num = 17941
keywords = ['patch']
message_count = 19.0
messages = ['188748', '188762', '188775', '188785', '188835', '188836', '188838', '189086', '189167', '189168', '189171', '189177', '190977', '220444', '220521', '220523', '220568', '244149', '275982']
nosy_count = 14.0
nosy_names = ['gvanrossum', 'barry', 'rhettinger', 'ncoghlan', 'eric.smith', 'eli.bendersky', 'BreamoreBoy', 'python-dev', 'sbt', 'serhiy.storchaka', 'dilettant', 'Christian.Tismer', 'josh.r', 'ctismer']
pr_nums = []
priority = 'low'
resolution = 'fixed'
stage = 'needs patch'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue17941'
versions = ['Python 3.6']

[sbt]

If the name is a qualified dotted name, it will be split and the first
part becomes the __module__.

That will not work correctly if the module name has a dot in it.

[ericvsmith]

I agree it should work the same as Enum, and I agree it should be possible to supply the module name. But wouldn't it be cleaner as:

Point = namedtuple('Point', 'x y z', module=__name__)

rather than:

Point = namedtuple(__name__ + '.Point', 'x y z')

?

[gvanrossum]

Agreed with Eric. We're already modifying PEP-435 to do it that way.

[elibendersky]

A question that came up while reviewing the new enum code: "module" or "module_name" for this extra argument? The former is shorter, but the latter is more correct in a way.

[gvanrossum]

Module, please. The class attribute is also called __module__ after all.

On Friday, May 10, 2013, Eli Bendersky wrote:

Eli Bendersky added the comment:

A question that came up while reviewing the new enum code: "module" or
"module_name" for this extra argument? The former is shorter, but the
latter is more correct in a way.

----------

---

Python tracker <report@bugs.python.org <javascript:;>>
<http://bugs.python.org/issue17941\>

---

[elibendersky]

On Fri, May 10, 2013 at 7:02 AM, Guido van Rossum <report@bugs.python.org>wrote:

Guido van Rossum added the comment:

Module, please. The class attribute is also called __module__ after all.

Makes sense. Thanks.

[rhettinger]

Marking this a low priority. I want to see how it pans out for Enums before adding a new parameter to the namedtuple API. Also, I would like to look at the test cases for Enum so I can see how you're writing tests that would fail without this parameter.

[gvanrossum]

I'd like to propose one slight tweak to the patch. (Also to enum.py.)

If no module name was passed and _getframe() fails, can you set the __module__ attribute to something that will cause pickling the object to fail? That would be much better than letting it pickle but then being unable to unpickle it.

(TBH I'm not sure how this should be accomplished, and if it can't, forget that I said it. But it would be nice.)

[sbt]

When pickling a class (or instance of a class) there is already a check
that the invariant

 getattr(sys.modules[cls.__module__], cls.__name__) == cls

holds.

 >>> import pickle
 >>> class A: pass
...
 >>> A.__module__ = 'nonexistent'
 >>> pickle.dumps(A())
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
_pickle.PicklingError: Can't pickle <class 'nonexistent.A'>: import of 
module 'nonexistent' failed

[gvanrossum]

Great, forget I said anything then.

LGTM to the patch, feel free to commit (with update to Misc/NEWS please).

[warsaw]

LGTM too. Needs test and docs.