4、str字符串数据类型

str：'alex' ,'1235443543',存储少量的数据。
        '[1,2,3]'
索引  切片  步长

# 索引
s = 'python12期'
s1 = s[0]
print(s1, type(s1))   #新的字符串 'p'
s2 = s[4]   # 'o'
s3 = s[-1]  # '期'
s4 = s[-3]  # '1'
print(s2, s3 ,s4)

#切片 :  顾头不顾尾
s = 'python12期'
s5 = s[0:2] #'py'
s6 = s[:2]  #'py'
s7 = s[1:-1] #'ython12'
s8 = s[1:]  #'ython12期'
print(s5, s6, s7, s8)


#步长 ：负数为倒着数，步长为正数，开头结尾由前到后，步长为负数，开头结尾由后到前，否则输出空
s = 'python12期'
s9 = s[-1:-5:-1] #'期21n'
s10 = s[1:5:2] #'yh'
s11 = s[-5:-1:1]
print(s9, s10, s11)