Python Challenge 第二题 字符串替换

将字符串里面的字母往后推两个，例如a变为c，z变为b，其它字符不变．

 1 def convert_string(aString):
 2         bString = ' '
 3         for i in aString:
 4             if ord('a')<=ord(i)<=ord('w') or ord('A')<=ord(i)<=ord('W'):
 5                 k = chr(ord(i)+2)
 6             elif i == 'y' or i == 'z':
 7                 k = chr(ord('a')+1+ord(i)-ord('z'))
 8             elif i == 'Y' or i == 'Z':
 9                 k = chr(ord('A')+1+ord(i)-ord('Z'))
10             else:
11                 k = i
12             bString += k
13         return bString

效果：