import re

def reserve(str_list, start, end):
  while start <= end:
    str_list[start], str_list[end] = str_list[end], str_list[start]
    end -= 1
    start += 1

str = ' I love china!  '
str_list = list(str)
print(str_list)
i = 0
print(len(str_list))

# 从前往后遍历list，如果碰到空格，就调用反转函数，不考虑单个字符情况
while i < len(str_list):
  if str_list[i] != ' ':
    start = i
    end = start + 1
    print(end)
    while (end < len(str_list)) and (str_list[end]!=' '):
      end += 1
    if end - start > 1:
      reserve(str_list, start, end-1)
      i = end
    else:
      i = end
  else:
    i += 1

print(str_list)
str_list.reverse()
print(''.join(str_list))

# 采用正则表达式操作
str_re = re.split(r'(\s+)',str)

str_re.reverse()
str_re = ''.join(str_re)
print(str_re)