字符串常用功能
1.capitalize:首字母大写
1 test = "feng"
2 首字母大写
3 v = test.capitalize()
4 print(v)
2.casefold,lower：所有变小写，casefold更牛逼，很多未知的相应变小写
1 v1 = test.casefold()
2 print(v1)
3 v2 = test.lower()
4 print(v2)
3.center:设置宽度，并居中
1 # 20 代指总长度
2 # * 空白未知填充，一个字符，可有可无
3 v = test.center(20,"中")
4 print(v)
4.count:去字符串中寻找，寻找子序列的出现次数
1 test = "fengfeng"
2 v = test.count('en')
3 print(v)
4
5 test = "fengfeng"
6 v = test.count('en',5,7)
7 print(v)
5.startswith,endswith:以什么什么结尾,以什么什么开始
1 test = "feng"
2 v = test.endswith('en')
3 v = test.startswith('en')
4 print(v)
6.find,index:find从开始往后找，找到第一个后，获取其位置，index找不到报错
1 test = "feng"
2 #未找到 -1
3 v = test.find('en')
4 print(v)
5
6 test = "feng"
7 v = test.index('feng')
8 print(v)
7.format,format_map:格式化，将一个字符串中的占位符替换为指定的值
1 test = 'i am {name}, age {a}'
2 print(test)
3 v = test.format(name='feng',a=19)
4 print(v)
5
6 test = 'i am {0}, age {1}'
7 print(test)
8 v = test.format('feng',19)
9 print(v)
10
11 #格式化，传入的值 {"name": 'feng', "a": 19}
12 test = 'i am {name}, age {a}'
13 v1 = test.format(name='df',a=10)
14 v2 = test.format_map({"name": 'feng', "a": 19})
8.isalnum字符串中是否只包含 字母和数字
1 test = "123"
2 v = test.isalnum()
3 print(v)