New submission from John Crawford <jtcrw...@gmail.com>:
At present, `collections.namedtuple` does not support `**` map unpacking
despite being a mapping style data structure. For example:
>>> from collections import namedtuple
>>> A = namedtuple("A", "a b c")
>>> a = A(10, 20, 30)
>>> def t(*args, **kwargs):
... print(f'args={args!r}, kwargs={kwargs!r}')
...
>>> t(*a)
args=(10, 20, 30), kwargs={}
>>> t(**a)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: t() argument after ** must be a mapping, not A
>>>
No doubt, the lack of current support is due to namespace conflicts that result
from trying to provide a `keys` method amidst also supporting attribute-style
access to the `namedtuple` class. As we can see, providing a `keys` attribute
in the `namedtuple` produces an interesting result:
>>> Record = namedtuple("Record", "title keys description")
>>> t(**Record(1, 2, 3))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: attribute of type 'int' is not callable
>>>
To me, this calls out a design flaw in the `**` unpacking operator where it
depends on a method that uses a non-system naming convention. It would make
far more sense for the `**` operator to utilize a `__keys__` method rather than
the current `keys` method. After all, the `__<methodname>__` naming convention
was introduced to avoid namespace conflict problems like this one.
----------
components: Library (Lib)
messages: 312218
nosy: John Crawford
priority: normal
severity: normal
status: open
title: Add ** Map Unpacking Support for namedtuple
type: enhancement
versions: Python 3.7, Python 3.8
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue32854>
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