blocks|key|1269670|text|我觉得你想要copy+module|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1269671|import+copy

x+=+copy.copy(y)++++++++#+make+a+shallow+copy+of+y
x+=+copy.deepcopy(y)++++#+make+a+deep+copy+of+y|code-block|syntax|javascript|1269672|控制复制的方式与控制pickle的方式大致相同。|1269673|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/library/copy.html|1|http://docs.python.org/library/pickle.html#module-pickle^0|6|B|0|0|0|A|6|1|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|K|3|-4|5|6|7|13|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]]]

I think you want the <a href="http://docs.python.org/library/copy.html" rel="noreferrer">copy module</a>

<pre><code>import copy

x = copy.copy(y) # make a shallow copy of y
x = copy.deepcopy(y) # make a deep copy of y
</code></pre>

you can control copying in much the same way as you control <a href="http://docs.python.org/library/pickle.html#module-pickle" rel="noreferrer">pickle</a>.

blocks|key|1484347|text|根据您的情况，我建议编写一个类方法(或者它可以是一个静态方法或一个单独的函数)，它以库的类的实例作为参数，并返回一个复制了所有适用属性的类的实例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1484348|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

For your situation, I would suggest writing a class method (or it could be a static method or a separate function) that takes as an argument an instance of the library's class and returns an instance of your class with all applicable attributes copied over.

blocks|key|1269827|text|在python中，可以使用默认参数定义复制构造函数。假设您希望普通构造函数运行函数non_copy_constructor(self)，而复制构造函数应该运行copy_constructor(self,+orig)。然后，您可以执行以下操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1269828|class+Foo:
++++def+__init__(self,+orig=None):
++++++++if+orig+is+None:
++++++++++++self.non_copy_constructor()
++++++++else:
++++++++++++self.copy_constructor(orig)
++++def+non_copy_constructor(self):
++++++++#+do+the+non-copy+constructor+stuff
++++def+copy_constructor(self,+orig):
++++++++#+do+the+copy+constructor

a=Foo()++#+this+will+call+the+non-copy+constructor
b=Foo(a)+#+this+will+call+the+copy+constructor|code-block|syntax|javascript|1269829|entityMap^0|15|Q|27|S|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

In python the copy constructor can be defined using default arguments. Lets say you want the normal constructor to run the function <code>non_copy_constructor(self)</code> and the copy constructor should run <code>copy_constructor(self, orig)</code>. Then you can do the following:

<pre><code>class Foo:
 def __init__(self, orig=None):
 if orig is None:
 self.non_copy_constructor()
 else:
 self.copy_constructor(orig)
 def non_copy_constructor(self):
 # do the non-copy constructor stuff
 def copy_constructor(self, orig):
 # do the copy constructor

a=Foo() # this will call the non-copy constructor
b=Foo(a) # this will call the copy constructor
</code></pre>

blocks|key|1269870|text|我通常实现的复制构造函数的一个简单示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1269871|import+copy

class+Foo:

++def+__init__(self,+data):
++++self._data+=+data

++@classmethod
++def+from_foo(cls,+class_instance):
++++data+=+copy.deepcopy(class_instance._data)+#+if+deepcopy+is+necessary
++++return+cls(data)|code-block|syntax|javascript|1269872|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

A simple example of my usual implementation of a copy constructor:

<pre><code>import copy

class Foo:

 def __init__(self, data):
 self._data = data

 @classmethod
 def from_foo(cls, class_instance):
 data = copy.deepcopy(class_instance._data) # if deepcopy is necessary
 return cls(data)
</code></pre>

blocks|key|1269939|text|建立在@Godsmith的train+of+thought之上，并满足@Zitrax对构造函数中所有属性进行数据复制的需求(我认为)：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1269940|class+ConfusionMatrix(pd.DataFrame):
++++def+__init__(self,+df,+*args,+**kwargs):
++++++++try:
++++++++++++#+Check+if+`df`+looks+like+a+`ConfusionMatrix`
++++++++++++#+Could+check+`isinstance(df,+ConfusionMatrix)`
++++++++++++#+But+might+miss+some+"ConfusionMatrix-elligible"+`DataFrame`s
++++++++++++assert((df.columns+==+df.index).all())
++++++++++++assert(df.values.dtype+==+int)
++++++++++++self.construct_copy(df,+*args,+**kwargs)
++++++++++++return
++++++++except+(AssertionError,+AttributeError,+ValueError):
++++++++++++pass
++++++++#+df+is+just+data,+so+continue+with+normal+constructor+here+...

++++def+construct_copy(self,+other,+*args,+**kwargs):
++++++++#+construct+a+parent+DataFrame+instance
++++++++parent_type+=+super(ConfusionMatrix,+self)
++++++++parent_type.__init__(other)
++++++++for+k,+v+in+other.__dict__.iteritems():
++++++++++++if+hasattr(parent_type,+k)+and+hasattr(self,+k)+and+getattr(parent_type,+k)+==+getattr(self,+k):
++++++++++++++++continue
++++++++++++setattr(self,+k,+deepcopy(v))|code-block|syntax|javascript|1269941|这个ConfusionMatrix类继承了一个pandas.DataFrame，并添加了大量其他需要重新计算的属性和方法，除非可以复制other矩阵数据。寻找解决方案就是我找到这个问题的原因。|style|CODE|1269942|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/27441776/623735|1|https://en.wikipedia.org/wiki/Confusion_matrix^0|D|G|0|0|0|2|F|N|G|1V|5|2|F|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|11|8|@$A|12|B|13|K|L]|$A|14|B|15|K|L]|$A|16|B|17|K|L]]|9|@$A|18|B|19|1|1A]]|C|$]]|$1|M|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

Building on @Godsmith's <a href="https://stackoverflow.com/a/27441776/623735">train of thought</a> and addressing @Zitrax's need (I think) to do the data copy for all attributes within the constructor:

<pre><code>class ConfusionMatrix(pd.DataFrame):
 def __init__(self, df, *args, **kwargs):
 try:
 # Check if `df` looks like a `ConfusionMatrix`
 # Could check `isinstance(df, ConfusionMatrix)`
 # But might miss some "ConfusionMatrix-elligible" `DataFrame`s
 assert((df.columns == df.index).all())
 assert(df.values.dtype == int)
 self.construct_copy(df, *args, **kwargs)
 return
 except (AssertionError, AttributeError, ValueError):
 pass
 # df is just data, so continue with normal constructor here ...

 def construct_copy(self, other, *args, **kwargs):
 # construct a parent DataFrame instance
 parent_type = super(ConfusionMatrix, self)
 parent_type.__init__(other)
 for k, v in other.__dict__.iteritems():
 if hasattr(parent_type, k) and hasattr(self, k) and getattr(parent_type, k) == getattr(self, k):
 continue
 setattr(self, k, deepcopy(v))
</code></pre>

This <a href="https://en.wikipedia.org/wiki/Confusion_matrix" rel="noreferrer"><code>ConfusionMatrix</code></a> class inherits a <code>pandas.DataFrame</code> and adds a ton of other attributes and methods that need to be recomputed unless the <code>other</code> matrix data can be copied over. Searching for a solution is how I found this question.

blocks|key|1270014|text|我也有类似的情况，不同之处在于新类只需要复制属性。因此，使用@Dunham的想法并为@meisterluk的建议添加一些特异性，@meisterluk的"copy_constructor“方法可以是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1270015|from+copy+import+deepcopy
class+Foo(object):
++++def+__init__(self,+myOne=1,+other=None):
++++self.two+=+2
++++if+other+<>+None:
++++++++assert+isinstance(other,+Foo),+"can+only+copy+instances+of+Foo"
++++++++self.__dict__+=+deepcopy(other.__dict__)
++++self.one+=+myOne

def+__repr__(self):
++++out+=+''
++++for+k,v+in+self.__dict__.items():
++++++++out+%2B=+'{:>4s}:+{},+{}\n'.format(k,v.__class__,v)
++++return+out

def+bar(self):
++++pass

foo1+=+Foo()
foo2+=+Foo('one',+foo1)

print+'\nfoo1\n',foo1
print+'\nfoo2\n',foo2|code-block|syntax|javascript|1270016|输出：|1270017|foo1
+two:+<type+'int'>,+2
+one:+<type+'int'>,+1


foo2
+two:+<type+'int'>,+2
+one:+<type+'str'>,+one|1270018|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I have a similar situation differing in that the new class only needs to copy attributes. Thus using @Dunham's idea and adding some specificity to @meisterluk's suggestion, @meisterluk's "copy_constructor" method could be:

<pre><code>from copy import deepcopy
class Foo(object):
 def __init__(self, myOne=1, other=None):
 self.two = 2
 if other &lt;&gt; None:
 assert isinstance(other, Foo), "can only copy instances of Foo"
 self.__dict__ = deepcopy(other.__dict__)
 self.one = myOne

def __repr__(self):
 out = ''
 for k,v in self.__dict__.items():
 out += '{:&gt;4s}: {}, {}\n'.format(k,v.__class__,v)
 return out

def bar(self):
 pass

foo1 = Foo()
foo2 = Foo('one', foo1)

print '\nfoo1\n',foo1
print '\nfoo2\n',foo2
</code></pre>

The output:

<pre><code>foo1
 two: &lt;type 'int'&gt;, 2
 one: &lt;type 'int'&gt;, 1


foo2
 two: &lt;type 'int'&gt;, 2
 one: &lt;type 'str'&gt;, one
</code></pre>

blocks|key|1270088|text|下面的解决方案可能会以简单的形式重复前面的一些解决方案。我不知道它是如何"pythocally“正确的，但它是有效的，并且在我使用它的特定情况下非常方便。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1270089|class+Entity:
++++def+__init__(self,+code=None,+name=None,+attrs=None):
++++++++self.code+=+code
++++++++self.name+=+name
++++++++self.attrs+=+{}+if+attrs+is+None+else+attrs


++++def+copy(self,+attrs=None):
++++++++new_attrs+=+{k:+v.copy()+for+k,+v+in+self.attrs.items()}+if+attrs+is+None+else+attrs
++++++++return+Entity(code=self.code,+name=self.name,+attrs=new_attrs)|code-block|syntax|javascript|1270090|用法：|1270091|new_entity+=+entity.copy()|1270092|这是一个更复杂的版本，允许干预复制过程。我只在一个地方使用过它。还要注意的是，self.attrs中包含的对象也有这样的“复制构造函数”。|offset|length|style|CODE|1270093|这个解决方案不是通用的，但是非常简单，并且提供了相当多的控制。|1270094|entityMap^0|0|0|0|0|13|A|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|Y|8|@$M|Z|N|10|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

The following solution probably repeats some of the previous ones in a simple form. I don't know how it is &quot;pythocally&quot; right, but it works and was quite convenient in the certain case I used it.
<pre><code>class Entity:
 def __init__(self, code=None, name=None, attrs=None):
 self.code = code
 self.name = name
 self.attrs = {} if attrs is None else attrs


 def copy(self, attrs=None):
 new_attrs = {k: v.copy() for k, v in self.attrs.items()} if attrs is None else attrs
 return Entity(code=self.code, name=self.name, attrs=new_attrs)
</code></pre>
Usage:
<pre><code>new_entity = entity.copy()
</code></pre>
This is a more complicated version that allows to interfere in the copying process. I used it in only one place. Also note that objects contained in <code>self.attrs</code> also have such kind of &quot;copying constructor&quot;.
This solution is not generic but is very simple and provides quite much control.

Is there a copy constructor in python ? If not what would I do to achieve something similar ?

The situation is that I am using a library and I have extended one of the classes there with extra functionality and I want to be able to convert the objects I get from the library to instances of my own class.

Copy constructor in python?

python中有复制构造函数吗？如果不是，我该怎么做才能达到类似的效果呢？情况是，我正在使用一个库，并且我已经扩展了其中一个具有额外功能的类，并且我希望能够将从库中获得的对象转换为我自己的类的实例。

问在python中复制构造函数？
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