[Python-ideas] Support other dict types for type.__dict__

Sven Marnach sven at marnach.net
Tue Feb 28 00:39:06 CET 2012

An easy way to create immutable instances is 'collections.namedtuple':

    X = namedtuple("X", "a b")
    x = X(a=4, b=2)
    x.a + x.b          # fine
    x.a = 5            # AttributeError: can't set attribute
    x.c = 5            # AttributeError: 'X' object has no attribute 'c'

Tricks using 'object.__setattr__()' etc. will fail since the instance
doesn't have a '__dict__'.  The only data in the instance is stored in
a tuple, so it's as immutable as a tuple.

You can also derive from 'X' to add further methods.  Remember to set
'__slots__' to an empty iterable to maintain immutability.


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