浅析Python中深拷贝和浅拷贝

Posted 2020-12-29

按照以下不同情况，在IDE中逐个解除注释，就明白了

import copy

"""
第一种情况，不可变类型变量，都是引用
"""
# a = 1
# a = (11, 222, 333)
# a = ‘string‘
# a = True
# b = a
#
# print(id(a))
# print(id(b))
#
# c =copy.copy(a)
# d = copy.deepcopy(a)
# print(id(c))
# print(id(d))

"""
第二种情况，可变类型变量，浅拷贝和深拷贝都开辟了空间
备注：[(1,2),3]外层可变，内层不可变，同此类型。
"""
# a = [2, 3, 4]
# # a = {2,5,6}
# # a = {"name": "jim"}
# b = a
# c =copy.copy(a)
# d = copy.deepcopy(a)
#
# print(id(a))
# print(id(b))
# print(id(c))
# print(id(d))
#
# # ................
# a.append(5)
# # ----------------
#
# print(a)
# print(b)
# print(c)
# print(d)

"""
第三种情况，内外层都是不可变类型的，深浅拷贝都是引用
"""
# a = ((1,2),)
# b = a
# c =copy.copy(a)
# d = copy.deepcopy(a)
#
# print(id(a))
# print(id(b))
# print(id(c))
# print(id(d))
#
#
# print(a)
# print(b)
# print(c)
# print(d)

"""
第四种情况，外层不可变，内层可变,因为浅拷贝对不可变类型只是指向了，也即引用了内存地址，深拷贝重新开辟了内存地址。
"""
# e = 1
# f = 2
# list1 = [e, f]
# a = (list1,) # a= ([1,2],)
# b = a
#
# print(id(a))
# print(id(b))
#
# c =copy.copy(a)
# d = copy.deepcopy(a)
# print(id(c))
# print(id(d))
#
# list1.append(8)
#
# print(id(a))
# print(id(b))
# print(id(c))
# print(id(d))
# print(a)
# print(b)
# print(c)
# print(d)

"""
第五种情况，外层可变，内层可变－－－－真正体现浅拷贝和深拷贝的差距，ａ[:]是一种浅拷贝。深浅拷贝都重新开辟了内存空间，浅拷贝的内层元素只是引用了内存地址，深拷贝的内层元素也重新开辟了内存空间。

"""
e = 1
f = 2
list1= [e,f]

g = 3
h = 4
list2 = [g,h]

a = [list1,list2]
b = a
c =copy.copy(a)
d = copy.deepcopy(a)

print(id(a))
print(id(b))
print(id(c))
print(id(d))

print(a)
print(b)
print(c)
print(d)

print("*" * 20)

# 改变ｅ或者ｆ的元素

list1.append(‘list1‘)

print(id(a))
print(id(b))
print(id(c))
print(id(d))

print(a)
print(b)
print(c)
print(d)

print("*" * 20)
a.append(‘a‘)

print(id(a))
print(id(b))
print(id(c))
print(id(d))

print(a)
print(b)
print(c)
print(d)