Python：创建类实例的副本

Question

我有一个我定义的 BipartiteGraph 类的实例“graph_main”。我现在需要的是保持这个实例不变，但创建这个类的另一个实例'graph1'，它与'graph_main'相同。但由于某种原因，graph_main 在我根本不使用它时也会不断变化。我是 Python 新手，就像几个星期一样。因此，如果有相关文档可以指导我学习 Python 中对象的范围，我会很感激。

MWE：

import numpy
import testBipartiteUtils
import random
#These are Bipartite graph parameters
N=30 #No of Bit Nodes
K=10 #No of Check Nodes 
rdeg=2 

graph_main = testBipartiteUtils.BipartGraph([])

for NodeIndex in range(0, K):
    graph_main.addBitNode(NodeIndex)#Adding Bit Node. No edges added

for NodeIndex in range(0, N):
    graph_main.addChkNode(NodeIndex)#Adding Check Node. No edges added

    attachments=random.sample(range(0,K),rdeg) 
    for j in attachments:
        graph_main.addEdge([j,NodeIndex])

for z in range(0,10):
    chan=[]
    for i in range(0,N):
        chan.append(0)

graph1=graph_main **#creating a new object identical to graph_main?**

PeelGraph=testBipartiteUtils.Peeling(graph1,chan)
PeelGraph.zeroStep()
print "graph_main Nodes are-",len(graph_main.BitNodes),len(graph_main.ChkNodes)
print "graph1 Nodes are-",len(graph1.BitNodes),len(graph1.ChkNodes)

del PeelGraph
print "z=",z

我提供了我的 Utils 文件以防有人想要运行它并查看它，但我非常怀疑这是否有必要。因此，我期望每个模拟在 graph_main（它是一个二分图类）中输出恒定数量的位和检查节点，因为我没有更改它。在这里，我假设 graph1=graph_main 创建了一个与现有 graph_main 相同的新对象。这是正确的，我的错误在别处吗？

testBipartiteUtils.py

import numpy

 class Edge:

 def __init__(self, n1, n2):
    """Constructor. Takes bit and check node IDs as arguments"""
    self.node1=n1
    self.node2=n2

def getNodes(self):
    """Returns a list containing the bit and check nodes for this edge"""
    return [self.node1, self.node2]

def hasNodes(self, n1, n2):
    """Takes two node IDs. Returns true if the IDs match the two nodes of this edge in that order."""
    if(self.node1==n1 and self.node2==n2):
        return True

    return False


 class BitNode:
""" Basic node class."""

def __init__(self, name):
    """Constructor. Takes a node ID"""
    self.ID=name
    self.neighbors=[]
    self.degree= 0

def addNeighbors(self, nbs):
    """Adds a list of neighbors to the current list. Takes a list of node IDs"""
    for i in range(0, len(nbs)):
        if(not nbs[i] in self.neighbors):
            self.neighbors.append(nbs[i])
            self.degree+=1

def getID(self):
    """Returns node ID"""
    return self.ID

def getNeighbors(self):
    """Returns list of neighbor IDs"""
    return self.neighbors


 class ChkNode:

def __init__(self, name):
    """Constructor. Takes a node ID"""
    self.ID=name
    self.neighbors=[]
    self.chan = int(-1)
    self.degree= 0


def addNeighbors(self, nbs):
    """Adds a list of neighbors to the current list. Takes a list of node IDs"""
    for i in range(0, len(nbs)):
        if(not nbs[i] in self.neighbors):
            self.neighbors.append(nbs[i])
            self.degree+=1

def getID(self):
    """Returns node ID"""
    return self.ID

def getNeighbors(self):
    """Returns list of neighbor IDs"""
    return self.neighbors


 class BipartGraph:
def __init__(self, eds):
    """Constructor. Takes a list of edge primitives, which is a list of two node IDs.
    Iterates through the edges, creates nodes for unique node IDs, and adds all edges and nodes.
    """
    self.size = 0
    self.BitNodes = []
    self.ChkNodes = []
    self.edges = []
    for i in range(0, len(eds)):
        self.addEdge(eds[i])


def containsEdge(self, edgep):
    """Checks for an edge in the graph. Takes an edge primitive, which is a list of two node IDs. First ID is bit node, second ID is of Check node"""
    for e in self.edges:
        if(e.hasNodes(edgep[0], edgep[1])):
            return True


def getBitNode(self, name):
    """Checks if a given Bit Node ID exists in the graph. If not, it creates and adds a Bit Node for the given ID. Returns the Bit Node"""
    for i in range(0, len(self.BitNodes)):
        if(self.BitNodes[i].getID()==name):
            return self.BitNodes[i]
    newNode = BitNode(name)
    self.BitNodes.append(newNode)
    return self.BitNodes[len(self.BitNodes)-1]

def getChkNode(self, name):
    """Checks if a given Chk Node ID exists in the graph. If not, it creates and adds a Chk Node for the given ID. Returns the Chk Node"""
    for i in range(0, len(self.ChkNodes)):
        if(self.ChkNodes[i].getID()==name):
            return self.ChkNodes[i]
    newNode = ChkNode(name)
    self.ChkNodes.append(newNode)
    return self.ChkNodes[len(self.ChkNodes)-1]

def getEdges(self):
    """Returns list of edges"""
    return self.edges

def addBitNode(self, name):
    """Adds a Bit node, based on Bit node ID"""
    newNode = BitNode(name)
    self.BitNodes.append(newNode)

def addChkNode(self, name):
    """Adds a Check node, based on node ID"""
    newNode = ChkNode(name)
    self.ChkNodes.append(newNode)

def addEdge(self, edgep):
    """Adds an edge into the graph, and updates neighbors & degrees of relevant nodes.
    Takes an edge primitive, a list of two node IDs
    """
    if(not self.containsEdge(edgep)):
        no1 = self.getBitNode(edgep[0])
        no2 = self.getChkNode(edgep[1])
        newEdge = Edge(edgep[0], edgep[1])
        self.edges.append(newEdge)
        no1.addNeighbors([no2.getID()])
        no2.addNeighbors([no1.getID()])

 class Peeling:
"""peeling decoder on a Bipartite graph class.
"""
def __init__(self, G,chan):
    """Constructor. Takes a graph and channel output vector as arguments"""
    self.graph=G
    for i in range(0,len(self.graph.ChkNodes)):
        self.graph.ChkNodes[i].chan=chan[i]
    self.deg1Chks=[]

def zeroStep(self):
    self.graph.BitNodes.pop(0)

def peelIter(self):
    self.graph.ChkNodes.pop(0)

Answer 1

使用deepcopy 函数创建具有新指针的相同实例（与浅拷贝相反，浅拷贝是指向同一对象的另一个变量）。

import copy

graph1= copy.deepcopy(graph_main)

Answer 2

我不确定，但你不能这样做吗？...

x = ClassName(arguments, arguments...)

dup_of_x = x

因此，x 存储 x 并且 dup_of_x 也存储 x