【python】索引和切片

s="abcdefghk"
print(s[0])   a
print(s[-1])  k
print(s[2])   c

s="abcdefgh"

print(s[:])   abcdefgh 
print(s[0:])  abcdefgh
print(s[0:-1]) abcdefg
print(s[0:-2]) abcdef
print(s[1:3]) bc
print(s[1:4]) bcd

print(s[0:4]) abcd

print(s[0:0]) 空字符 

print(s[0:5:2]) ace 步长为2 

print(s[4:0:-1]) 从4到0，取倒数值，不顾尾。edcb
 print(s[4::-1])  edcba
 print(s[-1::-1]) hgfedcba
 print(s[:])   abcdefgh
 print(s[::-1]) hgfedcba