# print("Hello world!")

# for i in range(1, 10):

# print(i)

def trim(s):

l = len(s)

if l == 0:

return ''

else:

x = y = 0

for i in range(l):

if s[i] != ' ':

x = i

break

for j in range((l - 1), -1, -1):

if s[j] != ' ':

y = j + 1

break

if x == y:

return ''

else:

return s[x:y]

# 测试:

if trim('hello ') != 'hello':

print('测试失败!')

elif trim(' hello') != 'hello':

print('测试失败!')

elif trim(' hello ') != 'hello':

print('测试失败!')

elif trim(' hello world ') != 'hello world':

print('测试失败!')

elif trim('') != '':

print('测试失败!')

elif trim(' ') != '':

print('测试失败!')

else:

print('测试成功!')