python 深浅拷贝，深浅拷贝的区别

深浅拷贝

• 说明：深浅拷贝是针对可变元素(引用类型)而言的，不可变元素不存在深浅拷贝的问题
• 示例：

  import copy
  ​
  # 值类型(不可变类型)
  a = 123
  a2 = a
  a3 = copy.copy(a)
  a4 = copy.deepcopy(a)
  ​
  print(a is a2)
  print(a is a3)
  print(a is a4)
  ​
  # 引用类型(可变类型)
  b = [1, 2, [3, 4]]
  b2 = b
  # 浅拷贝：只拷贝对象本身，内部元素只拷贝引用
  b3 = copy.copy(b)
  # 深拷贝：不但拷贝对象本身，还会拷贝内部元素
  b4 = copy.deepcopy(b)
  ​
  print(b is b2)
  print(b is b3)
  print(b is b4)
  ​
  b[0] = 100
  b[2][0] = 300
  print(b2)
  print(b3)
  print(b4)
  ​
  c = [1, 2, [3, 4]]
  # 浅拷贝
  d = c.copy()
  ​
  print(c is d)
  ​
  c[0] = 100
  c[2][0] = 200
  ​
  print(d)

  ​

标签： 拷贝 python