深淺拷貝

深淺拷貝

1、=

• 沒有產生新對象，都是內存地址的賦值

lst1 = [11, 22, 33, 44]
lst2 = lst1

print(id(lst1)) # 1916361712712
print(id(lst2)) # 1916361712712

lst1.append("hello")
print(lst1)  # [11, 22, 33, 44, 'hello']
print(lst2)  # [11, 22, 33, 44, 'hello']

dic1 = {"name": "Tom", "age": 18}
dic2 = dic1

print(id(dic1)) # 2020711820888
print(id(dic2)) # 2020711820888

dic1["hobby"]  = "football"

print(dic1)  # {'name': 'Tom', 'age': 18, 'hobby': 'football'}
print(dic2)  # {'name': 'Tom', 'age': 18, 'hobby': 'football'}

    對於list，set，dict來講，變量1 = 變量2，其實就至關於把變量2內容的內存地址交給變量1，並非複製一分內容，因此一變，都變。 

2、淺拷貝

• 優勢：省內存
• 缺點：只拷貝第一層內容
• 淺拷貝方法：copy()，對於list，還有lst[:]

lst1 = [11, 22, 33]
lst2 = lst1[:]

print(id(lst1))  # 1744651035720
print(id(lst2))  # 1744651035848

lst1.append(44)

print(lst1) # [11, 22, 33, 44]
print(lst2) # [11, 22, 33]

lst1 = [11, 22, 33, [44, 55]]
lst2 = lst1.copy()

print(id(lst1))  # 2081315824712
print(id(lst2))  # 2081316649864

lst1[3].append("hello")

print(lst1) # [11, 22, 33, [44, 55, 'hello']]
print(lst2) # [11, 22, 33, [44, 55, 'hello']]

3、深拷貝

• 深拷貝把內部元素徹底進行拷貝複製。

    深拷貝方法：

import copy

s2 = copy.deepcopy(s1)

import copy

lst1 = [11, 22, 33, [44, 55]]
lst2 = copy.deepcopy(lst1)

print(id(lst1))  # 1236356428872
print(id(lst2))  # 1236356430152

lst1[3].append("hello")

print(lst1) # [11, 22, 33, [44, 55, 'hello']]
print(lst2) # [11, 22, 33, [44, 55]]