[Python] How to make an immutable object in Python?

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 __setattr__, because then you can't even set attributes in the __init__. Subclassing a tuple is a trick that works:

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


But then you have access to the a and b variables through self[0] and self[1], which is annoying.

Is this possible in pure Python? If not, how would I do it with a C extension? Answers that work only in Python 3 are acceptable.

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