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POHow can I change in Python the return/input type of a list that is implemented as an class attribute?
 

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  1. POHow can I change in Python the return/input type of a list that is implemented as an class attribute?
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    <p><strong>EDIT (complete rephrase of the problem as the original version (see "original version", later) is misleading):</strong></p> <p>Here is the setting: I have a object which has a list of objects of type <code>&lt;class 'One'&gt;</code>. I would like to access this list but rather work with objects of type <code>&lt;class 'Two'&gt;</code> which is an enriched version of <code>&lt;class 'One'&gt;</code>.</p> <p>Background (1):</p> <ul> <li><code>One</code> could be an object that can be stored easily via a ORM. The ORM would handle the list depending on the data model</li> <li><code>Two</code> would be an object like <code>One</code> but enriched by many features or the way it can be accessed</li> </ul> <p>Background (2):</p> <ul> <li>I try to solve a SQLAlchemy related question that I asked <a href="https://stackoverflow.com/questions/8940802/how-to-integrate-sqlalchemy-and-a-subclassed-numpy-ndarray-smoothly-and-in-a-pyt">here</a>. So, the answer to the present question could be also a solution to that question changing return/input type of SQLAlchemy-lists.</li> </ul> <p>Here is some code for illustration:</p> <pre><code>import numpy as np class One(object): """ Data Transfere Object (DTO) """ def __init__(self, name, data): assert type(name) == str assert type(data) == str self.name = name self.data = data def __repr__(self): return "%s(%r, %r)" %(self.__class__.__name__, self.name, self.data) class Two(np.ndarray): _DTO = One def __new__(cls, name, data): dto = cls._DTO(name, data) return cls.newByDTO(dto) @classmethod def newByDTO(cls, dto): obj = np.fromstring(dto.data, dtype="float", sep=',').view(cls) obj.setflags(write=False) # Immutable obj._dto = dto return obj @property def name(self): return self._dto.name class DataUI(object): def __init__(self, list_of_ones): for one in list_of_ones: assert type(one) == One self.list_of_ones = list_of_ones if __name__ == '__main__': o1 = One('first object', "1, 3.0, 7, 8,1") o2 = One('second object', "3.7, 8, 10") my_data = DataUI ([o1, o2]) </code></pre> <p>How to implement a <code>list_of_twos</code> which operates on <code>list_of_ones</code> but provides the user a list with elements of type <code>Two</code>:</p> <pre><code>type (my_data.list_of_twos[1]) == Two &gt;&gt;&gt; True my_data.list_of_twos.append(Two("test", "1, 7, 4.5")) print my_data.list_of_ones[-1] &gt;&gt;&gt; One('test', '1, 7, 4.5') </code></pre> <hr> <p><strong>Original version of the question:</strong></p> <p>Here is an illustration of the problem:</p> <pre><code>class Data(object): def __init__(self, name, data_list): self.name = name self.data_list = data_list if __name__ == '__main__': my_data = Data ("first data set", [0, 1, 1.4, 5]) </code></pre> <p>I would like to access <code>my_data.data_list</code> via another list (e.g. <code>my_data.data_np_list</code>) that handles list-elements as a different type (e.g. as numpy.ndarray):</p> <pre><code>&gt;&gt;&gt; my_data.data_np_list[1] array(1) &gt;&gt;&gt; my_data.data_np_list.append(np.array(7)) &gt;&gt;&gt; print my_data.data_list [0, 1, 1.4, 5, 7] </code></pre>
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    1. USPhilipp der Rautenberg
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      1. POHow can I change in Python the return/input type of a list that is implemented as an class attribute?
      1. USPhilipp der Rautenberg
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      1. POHow can I change in Python the return/input type of a list that is implemented as an class attribute?
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    1. COnot sure I understood your question, but you may want to look at http://stackoverflow.com/questions/672172/how-to-use-python-map-and-other-functional-tools
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      1. POHow can I change in Python the return/input type of a list that is implemented as an class attribute?
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    2. COyou are missing a self argument
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      1. POHow can I change in Python the return/input type of a list that is implemented as an class attribute?
      1. USSimon
    3. COSorry, Chris, I hope my editing right now didn't interfere with your one... But yes, I referred to that question.
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      1. POHow can I change in Python the return/input type of a list that is implemented as an class attribute?
      1. USPhilipp der Rautenberg
 

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