[Python-ideas] a simple namespace type

[T.B.]

On 2012-05-27 19:08, Sven Marnach wrote:
 > Calvin Spealman schrieb am Sun, 27. May 2012, um 09:42:26 -0400:
 >> - record
 >> - flexobject
 >> - attrobject
 >> - attrdict
 >> - nameddict
 >> - namedobject
 >
 > Since the proposed type is basically an `object` allowing attributes,
 > another option would be `attrobject`.
 >
 > Adding an `__iter__()` method, as proposed earlier in this thread,
 > seems unnecessary; you can simply iterate over `vars(x)` for an
 > `attrobject` instance `x`.
 >

Is this whole class really necessary? As said before, this type is 
implemented numerous times:
* empty class (included in the Python Tutorial) [1]
* argparse.Namespace [2]
* multiprocessing.managers.Namespace [3]
* bunch (PyPI) that inherits from dict, instead of wrapping __dict__ [4]
* many more...

Each of them has a different semantics. Each is suited for a slightly 
different use case and they are so easy to implement. So you can 
customize to your liking - fields can or can't begin with "_", the later 
__repr__ comment or the color of the shed. Still, it seems they do not 
have a "killer feature" like namedtuple's efficiency.

Noticeable is how much they resemble a dict. Some let you iterate over 
the keys, test for equality and even all of the builtin dict methods 
(bunch). If you already use vars() for iteration, you might want a dict.

Funny that except for the easy "class Namespace: pass", the rest fail 
repr for recursive/self-referential objects:

 >>> from argparse/multiprocessing.managers/simplenamespace import Namespace
 >>> ns = Namespace()
 >>> ns.a = ns
 >>> repr(ns)
...
RuntimeError: maximum recursion depth exceeded

The next snippet use the fact that dict's __repr__ knows how to handle 
recursion to solve the RuntimeError problem:
def __repr__(self):
     return "{}({!r})".format(self.__class__.__name__, self.__dict__)


TB

[1] http://docs.python.org/dev/tutorial/classes.html#odds-and-ends
[2] http://hg.python.org/cpython/file/c1eab1ef9c0b/Lib/argparse.py#l1177
[3] 
http://hg.python.org/cpython/file/c1eab1ef9c0b/Lib/multiprocessing/managers.py#l913
[4] http://pypi.python.org/pypi/bunch