淺拷貝的時候，修改原來的對象，深拷貝的對象不會發生改變。

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對象的賦值

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對象的賦值實際上是對象之間的引用：當創建一個對象，然后將這個對象賦值給另外一個變量的時候，python并沒有拷貝這個對象，而只是拷貝了這個對象的引用。

aList = ["kel","abc",123] print(aList, id(aList)) bList = aListbList.append("add")print(aList, id(aList)) print(bList, id(bList)) (['kel', 'abc', 123], 139637569314688) (['kel', 'abc', 123, 'add'], 139637569314688) (['kel', 'abc', 123, 'add'], 139637569314688)

同樣 numpy 下的數據結構與數據類型的轉換（np.array vs. np.asarray）

np.array() 是深拷貝，np.asarray() 是淺拷貝

兩者主要的區別在于，array（默認）復制一份對象，asarray不會執行這一動作。

def asarray(a, dtype=None, order=None):return array(a, dtype, copy=False, order=order)

示例一

import numpy as np arr1=np.ones((3,3)) arr2=np.array(arr1) arr3=np.asarray(arr1) print(arr2 is arr1) print(arr3 is arr1) print('arr1:',arr1, id(arr1)) print('arr2:',arr2, id(arr2)) print('arr3:',arr3, id(arr3)) False True ('arr1:', array([[ 1., 1., 1.],[ 1., 1., 1.],[ 1., 1., 1.]]), 139637569303856) ('arr2:', array([[ 1., 1., 1.],[ 1., 1., 1.],[ 1., 1., 1.]]), 139637569303776) ('arr3:', array([[ 1., 1., 1.],[ 1., 1., 1.],[ 1., 1., 1.]]), 139637569303856)

示例二

import numpy as np arr1=np.ones((3,3)) arr2=np.array(arr1) arr3=np.asarray(arr1) arr1[1]=2 print('arr1:',arr1, id(arr1)) print('arr2:',arr2, id(arr2)) print('arr3:',arr3, id(arr3)) ('arr1:', array([[ 1., 1., 1.],[ 2., 2., 2.],[ 1., 1., 1.]]), 139637569303296) ('arr2:', array([[ 1., 1., 1.],[ 1., 1., 1.],[ 1., 1., 1.]]), 139637569303376) ('arr3:', array([[ 1., 1., 1.],[ 2., 2., 2.],[ 1., 1., 1.]]), 139637569303296)

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對象的復制

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當你想修改一個對象，而且讓原始的對象不受影響的時候，那么就需要使用到對象的復制，對象的復制可以通過三種方法實現：

a、 使用切片操作進行拷貝--slice operation b、 使用工廠函數進行拷貝，list/dir/set--factoryfunction c、 copy.copy（）--use copymodule

在復制的時候，使用的是淺拷貝，復制了對象，但是對象中的元素，依然使用引用。

person = ["name",["savings",100.00]] hubby = person[:] #切片操作 wifey = list(person) #使用工廠函數[id(x) for x in person,hubby,wifey] print("The person is:", person, id(person)) print("The hubby is:", hubby, id(hubby)) print("The wifey is:", wifey, id(wifey)) ('The person is:', ['name', ['savings', 100.0]], 139637569566984) ('The hubby is:', ['name', ['savings', 100.0]], 139637569544848) ('The wifey is:', ['name', ['savings', 100.0]], 139637569405656) print("The person inside is:", [id(x) for x in person]) print("The hubby inside is:", [id(x) for x in hubby]) print("The wifey inside is:", [id(x) for x in wifey]) ('The person inside is:', [139639860076144, 139637569544344]) ('The hubby inside is:', [139639860076144, 139637569544344]) ('The wifey inside is:', [139639860076144, 139637569544344])

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hubby[0] = "kel" wifey[0] = "jane" hubby[1][1] = 50.0 print("The person is:", person, id(person)) print("The hubby is:", hubby, id(hubby)) print("The wifey is:", wifey, id(wifey)) ('The person is:', ['name', ['savings', 50.0]], 139637570044992) ('The hubby is:', ['kel', ['savings', 50.0]], 139637569460344) ('The wifey is:', ['jane', ['savings', 50.0]], 139637569406160) print("The person inside is:", [id(x) for x in person]) print("The hubby inside is:", [id(x) for x in hubby]) print("The wifey inside is:", [id(x) for x in wifey]) ('The person inside is:', [139639860076144, 139637569810016]) ('The hubby inside is:', [139637569356104, 139637569810016]) ('The wifey inside is:', [139637569378272, 139637569810016])

在使用淺拷貝的時候，發現引用的id都是相同的，但是字符串的id卻發生了變化，是因為在python中，字符串是不可變的，從而在每次進行修改的時候，都是新建一個對象，從而引用發生了變化。

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copy模塊

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淺拷貝和深拷貝的操作都可以在copy模塊中找到，其實copy模塊中只有兩個函數可用，copy（）進行淺拷貝操作，而deepcopy（）進行深拷貝操作

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#1 import copy aList = [1,"kel",[1,2,3]] print("The aList is:", aList, id(aList))shadeList = copy.copy(aList) print("The shadeList is:", shadeList, id(shadeList))deepList = copy.deepcopy(aList) print("The deepList is:", deepList, id(deepList))aList[2].append("kel")print("The aList is:", aList, id(aList))print("The shadeList is:", shadeList, id(shadeList))print("The deepList is:", deepList, id(deepList)) ('The aList is:', [1, 'kel', [1, 2, 3]], 139639722291712) ('The shadeList is:', [1, 'kel', [1, 2, 3]], 139639722170344) ('The deepList is:', [1, 'kel', [1, 2, 3]], 139637569586096) ('The aList is:', [1, 'kel', [1, 2, 3, 'kel']], 139639722291712) ('The shadeList is:', [1, 'kel', [1, 2, 3, 'kel']], 139639722170344) ('The deepList is:', [1, 'kel', [1, 2, 3]], 139637569586096)

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#2 import copy aList = [1,"kel",[1,2,3]] print("The aList is:", aList, id(aList))shadeList = copy.copy(aList) print("The shadeList is:", shadeList, id(shadeList))deepList = copy.deepcopy(aList) print("The deepList is:", deepList, id(deepList))shadeList[2].append("kel")print("The aList is:", aList, id(aList))print("The shadeList is:", shadeList, id(shadeList))print("The deepList is:", deepList, id(deepList)) ('The aList is:', [1, 'kel', [1, 2, 3]], 139637569846448) ('The shadeList is:', [1, 'kel', [1, 2, 3]], 139637569406520) ('The deepList is:', [1, 'kel', [1, 2, 3]], 139637569407240) ('The aList is:', [1, 'kel', [1, 2, 3, 'kel']], 139637569846448) ('The shadeList is:', [1, 'kel', [1, 2, 3, 'kel']], 139637569406520) ('The deepList is:', [1, 'kel', [1, 2, 3]], 139637569407240)

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#3 import copy aList = [1,"kel",[1,2,3]] print("The aList is:", aList, id(aList))shadeList = copy.copy(aList) print("The shadeList is:", shadeList, id(shadeList))deepList = copy.deepcopy(aList) print("The deepList is:", deepList, id(deepList))deepList[2].append("kel") print("The deepList is:", deepList, id(deepList))print("The aList is:", aList, id(aList))print("The shadeList is:", shadeList, id(shadeList)) ('The aList is:', [1, 'kel', [1, 2, 3]], 139637569460776) ('The shadeList is:', [1, 'kel', [1, 2, 3]], 139637569461496) ('The deepList is:', [1, 'kel', [1, 2, 3]], 139637569585592) ('The deepList is:', [1, 'kel', [1, 2, 3, 'kel']], 139637569585592) ('The aList is:', [1, 'kel', [1, 2, 3]], 139637569460776) ('The shadeList is:', [1, 'kel', [1, 2, 3]], 139637569461496)

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參考文獻

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numpy 下的數據結構與數據類型的轉換（np.array vs. np.asarray）

numpy中array和asarray的區別

python中的深拷貝與淺拷貝

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