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POPython: problem with deepcopy(ing) a TypedList class inheriting from list and overriding append
 

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  1. POPython: problem with deepcopy(ing) a TypedList class inheriting from list and overriding append
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    <p>I don't understand why the new instance of the <code>TypeList</code> class does not have a <code>my_type</code> attribute.</p> <p>t.i.a. for any help</p> <p>Here is my code:</p> <pre><code>import copy class TypedList(list): def __init__(self, typeof, iterable=''): """ Initialize the typed list. Examples: tmp = TypedList(str, 'foobar') # OK tmp = TypedList('str', 'foobar') # FAIL! """ if not issubclass(type(typeof), object): raise TypeError('typeof must inherit from object') if type(typeof) is not type: raise TypeError('typeof, argument must be a python object type.\n' 'Not a string stating the type of python object.\n' 'Example: TypedList(str), not Typedlist("str")') self.my_type = typeof for item in iterable: if type(item) != self.my_type: raise TypeError('%s is of type %s; it should be type %s' % (item, type(item), self.my_type)) super(TypedList, self).__init__(iterable) def append(self, item): """ Append an item to the typed list. """ if type(item) != self.my_type: raise TypeError('item must be of type %s' % self.my_type) return super(TypedList, self).append(item) if __name__ == '__main__': foo = TypedList(str, 'test') bar = copy.deepcopy(foo) </code></pre> <p>Executing it returns this output:</p> <pre><code>$ python tl.py Traceback (most recent call last): File "tl.py", line 53, in &lt;module&gt; bar = copy.deepcopy(foo) File "/usr/lib/python2.6/copy.py", line 189, in deepcopy y = _reconstruct(x, rv, 1, memo) File "/usr/lib/python2.6/copy.py", line 329, in _reconstruct y.append(item) File "tl.py", line 46, in append if type(item) != self.my_type: AttributeError: 'TypedList' object has no attribute 'my_type' </code></pre>
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