我对列表副本有一些问题:
所以之后我得到了E0来自'get_edge',我做的副本E0通过调用'E0_copy = list(E0)'。我猜这里E0_copy是的较深的副本E0,我通过E0_copy了'karger(E)'。但是在主要功能上。 为什么'print E0[1:10]'for循环之前的结果与for循环之后的结果不同?
'get_edge'
'E0_copy = list(E0)'
E0_copy
E0_copy了'karger(E)'
'print E0[1:10]'for
下面是我的代码:
def get_graph(): f=open('kargerMinCut.txt') G={} for line in f: ints = [int(x) for x in line.split()] G[ints[0]]=ints[1:len(ints)] return G def get_edge(G): E=[] for i in range(1,201): for v in G[i]: if v>i: E.append([i,v]) print id(E) return E def karger(E): import random count=200 while 1: if count == 2: break edge = random.randint(0,len(E)-1) v0=E[edge][0] v1=E[edge][1] E.pop(edge) if v0 != v1: count -= 1 i=0 while 1: if i == len(E): break if E[i][0] == v1: E[i][0] = v0 if E[i][1] == v1: E[i][1] = v0 if E[i][0] == E[i][1]: E.pop(i) i-=1 i+=1 mincut=len(E) return mincut if __name__=="__main__": import copy G = get_graph() results=[] E0 = get_edge(G) print E0[1:10] ## this result is not equal to print2 for k in range(1,5): E0_copy=list(E0) ## I guess here E0_coypy is a deep copy of E0 results.append(karger(E0_copy)) #print "the result is %d" %min(results) print E0[1:10] ## this is print2
E0_copy不是深层副本。你不使用做出深层副本list()(两者list(...)并testList[:]很浅拷贝)。
list()(
list(...)
testList[:]
你copy.deepcopy(...)用于深度复制列表。
copy.deepcopy(...)
deepcopy(x, memo=None, _nil=[]) Deep copy operation on arbitrary Python objects.
请参阅以下代码段
>>> a = [[1, 2, 3], [4, 5, 6]] >>> b = list(a) >>> a [[1, 2, 3], [4, 5, 6]] >>> b [[1, 2, 3], [4, 5, 6]] >>> a[0][1] = 10 >>> a [[1, 10, 3], [4, 5, 6]] >>> b # b changes too -> Not a deepcopy. [[1, 10, 3], [4, 5, 6]]
现在看deepcopy操作
>>> import copy >>> b = copy.deepcopy(a) >>> a [[1, 10, 3], [4, 5, 6]] >>> b [[1, 10, 3], [4, 5, 6]] >>> a[0][1] = 9 >>> a [[1, 9, 3], [4, 5, 6]] >>> b # b doesn't change -> Deep Copy [[1, 10, 3], [4, 5, 6]]