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copied!<p>First of all, it's almost always a bad idea to do such a thing. If only reason why you want that is making sure you don't make typos - there are better tools for that (think IDE or pylint). If you are a 100% positive that you need such a thing, here are two ways to do it:</p> <p>First way - you can do this with using <code>__setattr__</code> method. See <a href="http://docs.python.org/2/reference/datamodel.html#object.__setattr__" rel="nofollow">python <code>__setattr__</code> documentation</a></p> <pre><code>class Person(object): def __init__(self, first_name, last_name): self.__dict__['first_name'] = first_name self.__dict__['last_name'] = last_name def __setattr__(self, name, value): if name in self.__dict__: super(Person, self).__setattr__(name, value) else: raise AttributeError("%s has no attribute %s" %(self.__class__.__name__, name)) </code></pre> <p>and output:</p> <pre><code>In [49]: a = Person(1, 2) In [50]: a.a = 2 --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) /usr/local/lib/python2.7/dist-packages/django/core/management/commands/shell.pyc in <module>() ----> 1 a.a = 2 /usr/local/lib/python2.7/dist-packages/django/core/management/commands/shell.pyc in __setattr__(self, name, value) 8 super(Person, self).__setattr__(name, value) 9 else: ---> 10 raise AttributeError("%s has no attribute %s" %(self.__class__.__name__, name)) AttributeError: Person has no attribute a </code></pre> <p>Alternatively, you can do this using <code>__slots__</code>(<a href="http://docs.python.org/2/reference/datamodel.html#slots" rel="nofollow">python <code>__slots__</code> documentation</a>):</p> <pre><code>class Person(object): __slots__ = ("first_name", "last_name") def __init__(self, first_name, last_name): self.first_name = first_name self.last_name = last_name </code></pre> <p>output:</p> <pre><code>In [32]: a = Person("a", "b") In [33]: a.first_name Out[33]: 'a' In [34]: a.a = 1 --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) /usr/local/lib/python2.7/dist-packages/django/core/management/commands/shell.pyc in <module>() ----> 1 a.a = 1 AttributeError: 'Person' object has no attribute 'a' </code></pre> <p>The first way is more flexible as it allows hacking this code even further through using <code>__dict__</code> directly, but that would be even more wrong than it is now. Second approach preallocates space for certain number of instance variables (references), which means less memory consumption.</p>

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