python基础类型数据的补充，以及循环中列表和字典的大小问题

字符串
1.capitalize 首字母大写其余变小写
s1 = “qweQQ”
print(s1.capitalize())
2.swapcase#大小写反转
print(s1.swapcase())
title 每个单词的首字母大写,只要被隔开
s2 = " how are3you"
print(s2.title())
3.center居中补齐
s1 = “qweQQ”
print(s1.center(11,"*"))
4.find只找元素第一个的索引值,找不到返回-1
s1 = “qweQQ”
print(s1.find(“Q”))
5.index只找元素第一个的索引值,找不到报错
s1 = “qweQQ”
print(s1.index(“Q”))

元组tuple,元组中只有一个元素,并且没有*逗号,那么他会以本身的数据类型显示
tul = (2)#2 <class ‘int’>
#tul = ([1,2,3])#[1, 2, 3] <class ‘list’>
print(tul,type(tul))
tu = (1,2,3,3,3)
print(tu.count(2))
print(tu.index(2))

列表list
1.index
l1 = [1,2,3,3,4]
print(l1.index(2))
2.sort
l1 = [123,1233,5123,1,2,431,1312]
#l1.sort(reverse = True)#默认升序排列,也可降序排列
l1.reverse()#翻转列表
print(l1)
相加,列表不去重
l1 = [1,23,231]
l2 = [1,2,23,“das”,“1123qawed”]
print(l1+l2)
print(l2*3)
列表去重
l1 = [1, 2, 3, 3, 4]
l1 =set(l1)
print(list(l1))

字典中删除索引为奇数的面试题
for index in range(len(l1)):
if (index) % 2 == 1:
l1.pop(index)
#正这删除元素会导致后续要处理的数据索引发生变化
print(l1)
del l1[1::2]
print(l1)
l1 = [1, 2, 3, 3, 4]
l1=l1[::-1]
print(l1)
倒叙法删除元素,已经处理后的数据索引发生变化,但不影响后续数据的索引
for index in range(len(l1)-1,-1,-1):
if index % 2 ==1:
l1.pop(index)
print(l1)
新建一个列表,将索引为偶数的取出来
l2 = []
for index in range(len(l1)):
if index % 2 == 0:
l2.append(l1[index])
print(l2)
*循环列表时千万不要改变列表的大小

字典
dic = {“name”:123,“age”:234}
dic.update(性别=“boy”,asd=“2213”)
dic.update(name=222)
dic.update([(1,“a”),(2,“b”),(3,“c”)])
print(dic)
dic1 = {“q”:1,“w”:2,“e”:3}
dic2 = {“q”:2,“r”:4}
dic1.update(dic2)
print(dic1)#更新,有则覆盖,无则增加
fromkeys
dic = dict.fromkeys(“adbdba”,100)
前一个元素是可迭代对象,后一个是共用的值,还会自动去除键的重复值
dic = dict.fromkeys([1,3,4,4],100)#{1: 100, 3: 100, 4: 100}
dic = dict.fromkeys([1,2,3,4],[])
dic[1].append(666)
print(dic)

*循环一个字典过程中如果改变了字典的大小,直接报错
dic = {“k1”:1,“k2”:2,“k3”:4,“q1”:5}
l1 = []
l = list(dic.keys())
for i in l :
if “k” in i:
dic.pop(i)
print(dic)

l1 = []
for key in dic:
if “k” in key:
l1.append(key)
for i in l1:
dic.pop(i)
print(dic)

所有数据类型都可以转换成布尔值
0,"",(),[],set(),None