deep-copy | 易学教程

Deepcopy on nested referenced lists created by list multiplication does not work

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问题 As much as I love Python, the reference and deepcopy stuff sometimes freaks me out. Why does deepcopy not work here: >>> import copy >>> a = 2*[2*[0]] >>> a [[0, 0], [0, 0]] >>> b = copy.deepcopy(a) >>> b[0][0] = 1 >>> b [[1, 0], [1, 0]] #should be: [[1, 0], [0, 1]] >>> I am using a numpy array as a workarround which I need later on anyway. But I really had hoped that if I used deepcopy I would not have to chase any unintended references any more. Are there any more traps where it does not

Does LINQ new up memory when creating returns

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问题 Does LINQ actually perform a deep copy of the results to a different list/array/etc, or does it simply give me a list/array/etc. composed of references to the original? 回答1: It's going to depend on if (and how) you use Select to project the results. If you do not create new objects in a projection then the result will reference the same objects as the original collection. If, however, you create new objects in the project then, obviously, they will not be the same. The collection returned

Java - Implement deep and shallow copy of an array

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问题 I am trying to understand the concept of shallow vs deep copy in Java. There is a lot of articles and Q&A about this subject, but whenever I try to implement these concepts in a real Java code, everything become unclear to me. One of the answers on which I base my understanding is in this link, where deep and shallow copying are explained via schemas. I will show you below my implementation for each case: Shallow copy: I took for my example the method System.arraycopy() as I read in many

Why isn't there a deep copy method in Ruby?

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问题 I am working on a solution for technical drawings (svg/ruby). I want to manipulate rectangles, and have an add! method in this class: class Rect def add!(delta) @x1+=delta ... # and so on self end end I also need an add method returning a Rect , but not manipulating self : def add(delta) r=self.dup/clone/"copy" # <-- not realy the 3 and no quotes, just in text here r.add! delta end dup and clone don't do my thing but: def copy; Marshal.load(Marshal.dump(self)); end does. Why does such a basic

Creating clone of an object not working with virtual base class

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问题 #include<iostream> using namespace std; class Something { public: int j; Something():j(20) {cout<<"Something initialized. j="<<j<<endl;} }; class Base { private: Base(const Base&) {} public: Base() {} virtual Base *clone() { return new Base(*this); } virtual void ID() { cout<<"BASE"<<endl; } }; class Derived : public Base { private: int id; Something *s; Derived(const Derived&) {} public: Derived():id(10) {cout<<"Called constructor and allocated id"<<endl;s=new Something();} ~Derived()

Deep copy System.Windows.Forms.WebBrowser Object/Restore State

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Essentially what I want to do is copy a WebBrowser object such that I can do the equivalent of "Open In New Tab" or "Open In New Window" actions, maintaining any posted data. I don't just want to navigate to the same URL as in the original WebBrowser object, rather I want to repeat the HttpWebRequest. Is this possible? How? I believe the WebBrowser object is a control, and therefore it has a window handle, which is going to cause issues if you try to clone it. I don't think you're going to get the behavior you want doing this. 来源： https://stackoverflow.com/questions/794117/deep-copy-system

How can I make a deepcopy of a function in Python?

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I would like to make a deepcopy of a function in Python. The copy module is not helpful, according to the documentation , which says: This module does not copy types like module, method, stack trace, stack frame, file, socket, window, array, or any similar types. It does “copy” functions and classes (shallow and deeply), by returning the original object unchanged; this is compatible with the way these are treated by the pickle module. My goal is to have two functions with the same implementation but with different docstrings. def A(): """A""" pass B = make_a_deepcopy_of(A) B.__doc__ = """B"""

When does pandas do pass-by-reference Vs pass-by-value when passing dataframe to a function?

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问题 def dropdf_copy(df): df = df.drop('y',axis=1) def dropdf_inplace(df): df.drop('y',axis=1,inplace=True) def changecell(df): df['y'][0] = 99 x = pd.DataFrame({'x': [1,2],'y': [20,31]}) x Out[204]: x y 0 1 20 1 2 31 dropdf_copy(x) x Out[206]: x y 0 1 20 1 2 31 changecell(x) x Out[208]: x y 0 1 99 1 2 31 In the above example dropdf() doesnt modify the original dataframe x while changecell() modifies x. I know if I add the minor change to changecell() it wont change x. def changecell(df): df = df

Cant copy construction be done without creating an explicit function in the pure virtual base class?

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My objective is to do a deep copy of a class, but a virtual class is causing trouble. #include<iostream> using namespace std; class Vir//pure virtual class { public: virtual void hi()=0; }; class Handler:public Vir { public: int i; Handler() {} Handler(int val):i(val) {} void hi() {cout<<"Value of i="<<i<<endl;} int getI() const {return i;} void setI(int j) {i=j;} }; class ControlPanel { public: Vir *v; ControlPanel(const ControlPanel& c)//copy constructor { v=new Handler; v->setI(c.getI()); } int getI()const {return v->getI();} void initialize() {v=new Handler(10);} void hi() {v->hi();}

Absolutely reference-free array copy with nested arrays

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At first I thought arr.slice(0) was doing a deep unreferenced copy, but it is actually doing just a shallow unreferenced copy, so if the array contains nested arrays, they are still referenced : var a = [1,2] var b = [3,4] var c = [a,b] var d = c.slice(0) d[0] === a // true, which means it is the /same/ object d[0][0] = "Hi!" a // ["Hi!", 2] (example source) The solution on the links provided is fairly easy when you know the structure of the array (just .slice(0) ing again the nested arrays will do the trick), but it gets complicated if you don't know how the structure of the nested arrays is.