Python：為什么我的原始列表在更新復制列表后會受到影響

Question

twoSeq=[['28.406925,77.285590', '28.409969,77.292279'],
    ['28.406925,77.285590', '28.402476,77.292956'],
    ['28.409969,77.292279', '28.403020,77.298851'],
    ['28.403020,77.298851', '28.392363,77.306091'],
    ['28.392363,77.306091', '28.378515,77.313990'],
    ['28.378515,77.313990', '28.367469,77.315308'],
    ['28.402476,77.292956', '28.399600,77.297313'],
    ['28.402476,77.292956', '28.397301,77.294096'],
    ['28.399600,77.297313', '28.392247,77.301909'],
    ['28.392247,77.301909', '28.392363,77.306091'],
    ['28.397301,77.294096', '28.399600,77.297313']]

def N_Seq(twoSeq):
    first=twoSeq.copy()
    last=twoSeq.copy()

    for i in range(len(first)):
        first[i].pop(0)
    print(first,"--------")
    for j in range(len(last)): 
        last[j].pop() 
    print(first)
N_Seq(twoSeq)

---

輸出：

[['28.409969,77.292279'], ['28.402476,77.292956'], ['28.403020,77.298851'], ['28.392363,77.306091'], ['28.378515,77.313990'], ['28.367469,77.315308'], ['28.399600,77.297313'], ['28.397301,77.294096'], ['28.392247,77.301909'], ['28.392363,77.306091'], ['28.399600,77.297313']] --------
[[], [], [], [], [], [], [], [], [], [], []]

Answer 1

list.copy創建列表的淺拷貝。 這意味着它會創建一個新列表並將對項目的引用插入其中。 在這種情況下，您應該使用copy.deepcopy ，它返回一個深層副本。

從文檔：

淺拷貝和深拷貝的區別僅與復合對象（包含其他對象的對象，如列表或類實例）有關：

• 淺拷貝構造一個新的復合對象，然后（在可能的范圍內）向其中插入對原始對象中的對象的引用。

• 深拷貝構造一個新的復合對象，然后遞歸地將原始對象中的對象的副本插入其中。

Answer 2

淺表副本

淺拷貝僅復制列表本身，它是對列表中對象的引用的容器。 如果包含自己的對象是可變的，並且其中一個被更改，則更改將反映在兩個列表中。

深拷貝

深復制列表與原始列表完全不同。

import copy
new_list = copy.deepcopy(old_list)

供參考。

Answer 3

import copy
twoSeq=[['28.406925,77.285590', '28.409969,77.292279'],
['28.406925,77.285590', '28.402476,77.292956'],
['28.409969,77.292279', '28.403020,77.298851'],
['28.403020,77.298851', '28.392363,77.306091'],
['28.392363,77.306091', '28.378515,77.313990'],
['28.378515,77.313990', '28.367469,77.315308'],
['28.402476,77.292956', '28.399600,77.297313'],
['28.402476,77.292956', '28.397301,77.294096'],
['28.399600,77.297313', '28.392247,77.301909'],
['28.392247,77.301909', '28.392363,77.306091'],
['28.397301,77.294096', '28.399600,77.297313']]

def N_Seq(twoSeq):
    first=copy.deepcopy(twoSeq)
    last=copy.deepcopy(twoSeq)

    for i in range(len(first)):
        first[i].pop(0)
    print(first,"--------")
    for j in range(len(last)): 
        last[j].pop() 
    print(first)
N_Seq(twoSeq)