0x3 Python学习之路之Python列表copy

初认识copy

import copy

names = ["China", "ShanDong", "LiaoCheng", "University"]
names2 = names.copy()
print(names)
print(names2)
#['China', 'ShanDong', 'LiaoCheng', 'University']
#['China', 'ShanDong', 'LiaoCheng', 'University']

修改列表信息，认识copy

import copy
names = ["China", "ShanDong", "LiaoCheng", "University"]
names2 = names.copy()
names[2] = "DongChang"
print(names,names2)
#['China', 'ShanDong', 'DongChang', 'University'] ['China', 'ShanDong', 'LiaoCheng', 'University']

浅copy

names = ["China", "ShanDong", "LiaoCheng",["GJHe","ymxowgk"] ,"University"]
names2 = names.copy()
names[2] = "DongChang"
print(names)
print(names2)
#['China', 'ShanDong', 'DongChang', ['GJHe', 'ymxowgk'], 'University'] ['China', 'ShanDong', 'LiaoCheng', ['GJHe', 'ymxowgk'], 'University']
#拷贝的内存地址

浅copy的三种方式：

person = ['name',['money',100]]
p1 = copy.copy(person)
p2 = person[:]
p3 = list(person)

浅copy应用

创建联合账号，例如张三和马荣是一对夫妻关系，他俩有个共同银行账户，当张三取钱时，马荣账户跟随改变

person = ['name',['money',100]]
p1 = person[:]
p2 = person[:]

p1[0] = "张三"
p2[0] = "马荣"

p1[1][1] = 50

print(p1)
print(p2)
#输出
#['张三', ['money', 50]]
#['马荣', ['money', 50]]

字符串，列表赋值更新区别

#字符串
a = 1;
b = a;
a = 2;
print("a:",a,"b:",b)
#a: 2 b: 1


#列表
a = [1,2,4]
b = a
a[1] = 3333
print("a:",a,"b:",b)
#a: [1, 3333, 4] b: [1, 3333, 4]

深copy

names = ["China", "ShanDong", "LiaoCheng",["GJHe","ymxowgk"] ,"University"]
names2 = copy.deepcopy(names)
print(names)
print(names2)
names[2] = "DongChang"
names[3][0] = "gaojihe"
print(names)
print(names2)

#['China', 'ShanDong', 'LiaoCheng', ['GJHe', 'ymxowgk'], 'University']
#['China', 'ShanDong', 'LiaoCheng', ['GJHe', 'ymxowgk'], 'University']
#['China', 'ShanDong', 'DongChang', ['gaojihe', 'ymxowgk'], 'University']
#['China', 'ShanDong', 'LiaoCheng', ['GJHe', 'ymxowgk'], 'University']

#这样复制就不会改变子列表的值了，是因为deepcopy将子列表也复制了一份
#注：不过，deepcopy方法，如果数据很大，完全复制就是存储两份数据，占用内存，慎用！

遍历列表元素

names = ["China", "ShanDong", "LiaoCheng", "University"]
for i in names :
    print(i)


#输出
China
ShanDong
LiaoCheng
University

列表跳着切片

names = ["China", "ShanDong", "LiaoCheng", "University"]


print(names[0:-1:2])#[::2]

#['China', 'LiaoCheng']