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POmemory management with objects and lists in python
 

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    <p>I am trying to understand how exactly assignment operators, constructors and parameters passed in functions work in python specifically with lists and objects. I have a class with a list as a parameter. I want to initialize it to an empty list and then want to populate it using the constructor. I am not quite sure how to do it.</p> <p>Lets say my class is --</p> <pre><code>class A: List = [] # Point 1 def __init1__(self, begin=[]): # Point 2 for item in begin: self.List.append(item) def __init2__(self, begin): # Point 3 List = begin def __init3__(self, begin=[]): # Point 4 List = list() for item in begin: self.List.append(item) listObj = A() del(listObj) b = listObj </code></pre> <p>I have the following questions. It will be awesome if someone could clarify what happens in each case --</p> <ol> <li><p>Is declaring an empty like in Point 1 valid? What is created? A variable pointing to NULL?</p></li> <li><p>Which of Point 2 and Point 3 are valid constructors? In Point 3 I am guessing that a new copy of the list passed in (begin) is not made and instead the variable List will be pointing to the pointer "begin". Is a new copy of the list made if I use the constructor as in Point 2?</p></li> <li><p>What happens when I delete the object using del? Is the list deleted as well or do I have to call del on the List before calling del on the containing object? I know Python uses GC but if I am concerned about cleaning unused memory even before GC kicks in is it worth it?</p></li> <li><p>Also assigning an object of type A to another only makes the second one point to the first right? If so how do I do a deep copy? Is there a feature to overload operators? I know python is probably much simpler than this and hence the question.</p></li> </ol> <p>EDIT: 5. I just realized that using Point 2 and Point 3 does not make a difference. The items from the list begin are only copied by reference and a new copy is not made. To do that I have to create a new list using list(). This makes sense after I see it I guess.</p> <p>Thanks!</p>
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    1. COHave you read [the Python tutorial](http://docs.python.org/tutorial/)?
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    2. CONote `List = []` and `__init1__(self, begin=[])` will result [same list among all objects of the class](http://stackoverflow.com/questions/1132941/least-astonishment-in-python-the-mutable-default-argument). This most likely not the behavior which you are expecting!
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    3. CO@BrenBarn - I did initially to get the syntax and then jumped into code hoping to learn along the way. I think I understand it better now. Please see my edit above.
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