Python基礎之深淺copy
阿新 • • 發佈:2018-09-12
deepcopy 示例 3.2 一致性 code 結果 epc 完全 pri
1. 賦值
lst1 = [1, 2, 3, ["a", "b", "c"]]
lst2 = lst1
lst1[0] = 11
print(lst1) #[11, 2, 3, [‘a‘, ‘b‘, ‘c‘]]
print(lst2) #[11, 2, 3, [‘a‘, ‘b‘, ‘c‘]]
lst1[3][0] = "d"
print(lst1) #[11, 2, 3, [‘d‘, ‘b‘, ‘c‘]]
print(lst2) #[11, 2, 3, [‘d‘, ‘b‘, ‘c‘]]
對於賦值運算來說,lst1和lst2指向的是同一個內存地址,所以它們是一樣的。
2. 淺copy
2.1 示例1
lst1 = [1, 2, 3, ["a", "b", "c"]]
lst2 = lst1.copy()
print(lst1, id(lst1))
print(lst2, id(lst2))
執行結果為:
[1, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 48285736
[1, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 48285776
2.2 示例二
lst1 = [1, 2, 3, ["a", "b", "c"]] lst2 = lst1.copy() lst1[0] = 11 print(lst1, id(lst1)) print(lst2, id(lst2))
執行結果為:
[11, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 48285736
[1, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 48285776
2.3 示例三
lst1 = [1, 2, 3, ["a", "b", "c"]]
lst2 = lst1.copy()
lst1[3][0] = "d"
print(lst1, id(lst1))
print(lst2, id(lst2))
執行結果為:
[1, 2, 3, [‘d‘, ‘b‘, ‘c‘]] 48285536
[1, 2, 3, [‘d‘, ‘b‘, ‘c‘]] 48285736
2.4 總結
對於淺copy來所,第一層創建的是新的內存地址,而從第二層開始,指向的都是同一個內存地址。
所以,對於第二層以及更深的層數來說,保持一致性。
3. 深拷貝(deepcopy)
3.1 示例一
import copy
lst1 = [1, 2, 3, ["a", "b", "c"]]
lst2 = copy.deepcopy(lst1)
print(lst1, id(lst1))
print(lst2, id(lst2))
執行結果為:
[1, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 54249392
[1, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 54249992
3.2 示例二
import copy
lst1 = [1, 2, 3, ["a", "b", "c"]]
lst2 = copy.deepcopy(lst1)
lst1[0] = 11
print(lst1, id(lst1))
print(lst2, id(lst2))
執行結果為:
[11, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 48678832
[1, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 48679432
3.3 示例三
import copy
lst1 = [1, 2, 3, ["a", "b", "c"]]
lst2 = copy.deepcopy(lst1)
lst1[3][0] = "d"
print(lst1, id(lst1))
print(lst2, id(lst2))
執行結果為:
[1, 2, 3, [‘d‘, ‘b‘, ‘c‘]] 46516144
[1, 2, 3, [‘a‘, ‘b‘, ‘c‘]] 46516744
3.4 總結
對於deepcopy來說,兩個是完全獨立的,改變任意一個的任何元素(無論多少層),另一個絕對不改變。
Python基礎之深淺copy