Python入门（三）

LIST
列表是一个数据的集合，集合内可以放任何数据类型，可对集合进行方便的增删改查操作。

1. list类型的声明
   months=[]
   print(type(months))
   names=[‘shanshan’,’longting’]

2. append函数，list中添加元素
   months.append(1)
   months.append(“January”)
   months.append(2)
   months.append(“February”)

3. 在list中找一个值,创建list的时候就产生了对应的索引，从0开始
   countries=[]
   temperatures=[]
   countries.append(“china”)
   countries.append(“india”) countries.append(“united states”)
   temperatures.append(30.5)
   temperatures.append(25.0)
   temperatures.append(15.1)
   china=countries[0]
   china_temperature=temperature[0]

4. len函数，表示list中有多少元素
   int_months=[1,2,3,4,5,6,7,8,9,10,11,12]
   length=len(int_months)
   index=len(int_months)-1
   last_value=int_months[index]
   print(last_value) #12
   print(int_months[-1]) #12

   -1代表倒数第一个元素，-2代表倒数第二个元素……

5. 切片，取list中某个片段
   months=[“jan”,”feb”,”mar”,”apr”,”may”,”jun”,”jul”]
   two_four=months[2:4] #values at index 2,3,but not 4，取头不取尾
   print(two_four) #[“mar”,”apr”]
   three_six=months[3:] #一直取到尾
   print(three_six) #[“apr”,”may”,”jun”,”jul”]

two_four=months[2:4:2] #第二个2代表隔两个取值，步长

1. index函数,找索引值

countries=[]
countries.append("china")
countries.append("india")            countries.append("united states")
a=countries.index(India)
country=countries[a]

7.count函数，统计个数

n2=['shanshan','longting','alex',1,3,4,4,5,6,7,7,8,8,9,9,0,0,2,3,4,4]
num=n2.count(4)   #统计4有几个

8.插入，insert函数，给索引i处插入值

n2=['shanshan','longting','alex',1,3,4,4,5,6,7,7,8,8,9,]
n2.insert(0,'abc')
#['abc','shanshan','longting','alex',1,3,4,4,5,6,7,7,8,8,9,4]
n2[2]='peiqi'  #修改
n2[2:4]='peiqi'  #批量修改

9.pop函数，删除最后一个，remove函数删除，del函数批量删除

n2=['shanshan','longting','alex',1,3,4,4,5,6,7,7,8,8,9,]
n2.pop()
n2.remove('shanshan')
del n2[2:4]

10.循环

n2=['shanshan','longting','alex',1,3,4,4,5,6,7,7,8,8,9,]
for i in n2:
    print(i)

11.排序，sort函数，按ascii码排序；reverse倒序排序；

n2.sort()

12.扩展，+或者extend函数

n1=[1,3,4]
n2=['shanshan','longting','alex',1,3,4,4,5,6,]
n=n2+n1
n2.extend(n1)
#['shanshan','longting','alex',1,3,4,4,5,6,1,3,4]

13.clear函数，copy函数

n2.clear()
n3=n2.copy()

14.枚举enumerate函数

names=['alex','shanshan']
for index,i in enumerrate(names):
    print(index,i)

#0 alex
#1 shanshan