Python统计字符个数，计算结果一直不对怎么办，麻烦大佬捞捞看看哪里错了

n=input("请输入一串字符：")
letter=dight=blank=others=0
for i in n:
if ord('a')<=ord('i')<=ord('z') or ord('A')<=ord('i')<=ord('Z'):
letter=letter+1
elif ord('0')<=ord('i')<=ord('9'):
dight=dight+1
elif ord('i')==ord(' '):
blank=blank+1
else:
others=others+1
print("这串字符中字母的个数为：{},数字的个数为：{},空格的个数为：{},其他字符的个数为：{}".format(letter,dight,blank,others))