import copy
a = "deepak"
b = 1, 2, 3, 4
c = [1, 2, 3, 4]
d = {1: 10, 2: 20, 3: 30}
a1 = copy.copy(a)
b1 = copy.copy(b)
c1 = copy.copy(c)
d1 = copy.copy(d)
print("immutable - id(a)==id(a1)", id(a) == id(a1))
print("immutable - id(b)==id(b1)", id(b) == id(b1))
print("mutable - id(c)==id(c1)", id(c) == id(c1))
print("mutable - id(d)==id(d1)", id(d) == id(d1))
我得到了以下结果:
immutable - id(a)==id(a1) True
immutable - id(b)==id(b1) True
mutable - id(c)==id(c1) False
mutable - id(d)==id(d1) False
如果我执行深度复制:
a1 = copy.deepcopy(a)
b1 = copy.deepcopy(b)
c1 = copy.deepcopy(c)
d1 = copy.deepcopy(d)
结果是一样的:
immutable - id(a)==id(a1) True
immutable - id(b)==id(b1) True
mutable - id(c)==id(c1) False
mutable - id(d)==id(d1) False
如果我从事赋值操作:
a1 = a
b1 = b
c1 = c
d1 = d
那么结果是:
immutable - id(a)==id(a1) True
immutable - id(b)==id(b1) True
mutable - id(c)==id(c1) True
mutable - id(d)==id(d1) True
有没有人能解释一下到底是什么造成了副本之间的不同?它是与可变和不可变对象相关的吗?如果是这样的话,你能给我解释一下吗?
发布于 2013-06-22 10:25:27
对于不可变对象,不需要复制,因为数据永远不会改变,所以Python使用相同的数据;is总是相同的。对于可变对象,因为它们可能会更改,所以浅复制会创建一个新对象。
深度复制与嵌套结构相关。如果你有列表的列表,那么deepcopy copies
嵌套的列表,所以它是一个递归的副本。使用just copy,你有了一个新的外部列表,但内部列表是引用。
分配不会复制。它只是设置对旧数据的引用。因此,您需要复制以创建具有相同内容的新列表。
发布于 2017-06-09 05:42:16
让我们在一个图形示例中看看如何执行以下代码:
import copy
class Foo(object):
def __init__(self):
pass
a = [Foo(), Foo()]
shallow = copy.copy(a)
deep = copy.deepcopy(a)
发布于 2018-03-25 16:11:34
下面的代码演示了赋值、使用copy方法的浅复制、使用(slice)的浅复制和深度复制之间的区别。下面的示例使用嵌套列表,使差异更加明显。
from copy import deepcopy
########"List assignment (does not create a copy) ############
l1 = [1,2,3, [4,5,6], [7,8,9]]
l1_assigned = l1
print(l1)
print(l1_assigned)
print(id(l1), id(l1_assigned))
print(id(l1[3]), id(l1_assigned[3]))
print(id(l1[3][0]), id(l1_assigned[3][0]))
l1[3][0] = 100
l1.pop(4)
l1.remove(1)
print(l1)
print(l1_assigned)
print("###################################")
########"List copy using copy method (shallow copy)############
l2 = [1,2,3, [4,5,6], [7,8,9]]
l2_copy = l2.copy()
print(l2)
print(l2_copy)
print(id(l2), id(l2_copy))
print(id(l2[3]), id(l2_copy[3]))
print(id(l2[3][0]), id(l2_copy[3][0]))
l2[3][0] = 100
l2.pop(4)
l2.remove(1)
print(l2)
print(l2_copy)
print("###################################")
########"List copy using slice (shallow copy)############
l3 = [1,2,3, [4,5,6], [7,8,9]]
l3_slice = l3[:]
print(l3)
print(l3_slice)
print(id(l3), id(l3_slice))
print(id(l3[3]), id(l3_slice[3]))
print(id(l3[3][0]), id(l3_slice[3][0]))
l3[3][0] = 100
l3.pop(4)
l3.remove(1)
print(l3)
print(l3_slice)
print("###################################")
########"List copy using deepcopy ############
l4 = [1,2,3, [4,5,6], [7,8,9]]
l4_deep = deepcopy(l4)
print(l4)
print(l4_deep)
print(id(l4), id(l4_deep))
print(id(l4[3]), id(l4_deep[3]))
print(id(l4[3][0]), id(l4_deep[3][0]))
l4[3][0] = 100
l4.pop(4)
l4.remove(1)
print(l4)
print(l4_deep)
print("##########################")
print(l4[2], id(l4[2]))
print(l4_deep[3], id(l4_deep[3]))
print(l4[2][0], id(l4[2][0]))
print(l4_deep[3][0], id(l4_deep[3][0]))
https://stackoverflow.com/questions/17246693
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