Python基础语法(三)列表、集合

列表的定义

列表的定义可以是相同类型的，也可以是不同类型的

names = ["老王","老李","老刘"]
names = [12,18,"老王"]

添加

append

names = ["老王","老李","老刘"]
names.append("老赵")  #打印信息 ["老王","老李","老刘","老赵"]

insert

names = ["老王","老李","老刘"]
names.insert(0,"老赵") #打印信息 ["老赵","老王","老李","老刘"]

+

names1 =   ["老王","老李","老刘"]
names2 = ["八戒","悟空","沙僧"]
names = names1 + names2

extend 合并括号中的列表到调用的列表中

names1 =   ["老王","老李","老刘"]
names2 = ["八戒","悟空","沙僧"]
name1.extend(name2) #将names2的内容合并到names1中

extend append 区别：
1.extend 将列表中元素一个一个添加进入
2.append将列表作为一个元素进行添加

删除

pop 弹出最后一个元素

names1 =   ["老王","老李","老刘"]
names1.pop() #打印老刘
print(names1) #["老王","老李"]

remove 删除指定元素

names1 =   ["老王","老李","老刘"]
names1.remove("老王") # ["老李","老刘"]

del 通过下标删除

names =   ["老王","老李","老刘"]
del names[0] #["老李","老刘"]
del names[0:] #[]

修改

names =   ["老王","老李","老刘"]
names[0] = "老赵"

查询

in
not in

names =   ["老王","老李","老刘"]
if "老赵" in names:
    print("在里面")
if "老赵" not in names:
    print("不在里面")

排序

sort

nums = [1,2,3,23,3,345,323,567,8,9,34]
nums.sort() #从小到大
nums.sort(reverse=True) #从大到小
print(nums)

字典排序

infos = [{"name":"laowang","old":12},{"name":"banzhang","old":14},{"name":"xiaoming","old":2}]

infos.sort(key=lambda x:x["old"],reverse=True) #x 是{"name":"laowang","old":12}字典的引用，x["old"]取old的值，`:`后面是返回值

print(infos) #[{"name":"banzhang","old":14},{"name":"laowang","old":12},{"name":"xiaoming","old":2}]

逆序

reverse

nums = [1,2,34]
nums.reverse() 
print(nums) #[34,2,1]

列表的生成式

python2 中
a = range(1,5) #[1,2,3,4] 有风险，如果range很大，会内存崩溃

python3中
range(1,5) 就是range(1,5)，只有取当需要的时候才将值取出

a = [i for i in range(1,5)] #a = [1,2,3,4] i执行多少遍，前面的i就有多少个
a = [11 for i in range(1,5)] #a = [11,11,11,11]
a = [i for i in range(1,5) if i%2 == 0] #a = [2,4]
a = [i for i in range(3) for j in range(2)] #a = [0,0,1,1,2,2]
a = [(i,j) for i in range(2) for j in range(2)] #a = [(0,0),(0,1),(1,0),(1,1)]

集合

集合的定义格式：{元素1，元素2，...}
集合中的数据不能相同
允许增删改查

a = {11,22,33,11,22,33}
print(a) #{11,22,33}
type(a) #set

列表去重

a = [1,2,3,4,5,6,2,4]
b = []
for i in a
  if i not in b
    b.append(i)

a = [1,2,3,4,5,6,2,4]
f = set(a)
b = list[f]