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POHow to make an immutable object in Python?
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copied!<p>Although I have never needed this, it just struck me that making an immutable object in Python could be slightly tricky. You can't just override <a href="https://docs.python.org/3/reference/datamodel.html#object.__setattr__" rel="noreferrer"><code>__setattr__</code></a>, because then you can't even set attributes in the <a href="https://docs.python.org/3/reference/datamodel.html#object.__init__" rel="noreferrer"><code>__init__</code></a>. Subclassing a tuple is a trick that works:</p> <pre><code>class Immutable(tuple): def __new__(cls, a, b): return tuple.__new__(cls, (a, b)) @property def a(self): return self[0] @property def b(self): return self[1] def __str__(self): return "<Immutable {0}, {1}>".format(self.a, self.b) def __setattr__(self, *ignored): raise NotImplementedError def __delattr__(self, *ignored): raise NotImplementedError </code></pre> <p>But then you have access to the <code>a</code> and <code>b</code> variables through <code>self[0]</code> and <code>self[1]</code>, which is annoying.</p> <p>Is this possible in Pure Python? If not, how would I do it with a C extension?</p> <p>(Answers that work only in Python 3 are acceptable).</p> <p><strong>Update:</strong> </p> <p>So subclassing tuple is the way to do it in Pure Python, which works well except for the additional possibility of accessing the data by <code>[0]</code>, <code>[1]</code> etc. So, to complete this question all that is missing is howto do it "properly" in C, which I suspect would be quite simple, by just not implementing any <code>geititem</code> or <code>setattribute</code>, etc. But instead of doing it myself, I offer a bounty for that, because I'm lazy. :)</p>

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