Python 切片：利用切片操作，實現一個trim()函式，去除字串首尾的空格，不呼叫str的strip()方法。

# Basic Version:
def trim(s):
    length = len(s)

    if length > 0:
        for i in range(length):
            if s[i] != ' ':
                break;
        j = length-1;
        while s[j] == ' ' and j >= i:
            j -= 1
        s = s[i:j+1]

    return s

# Improvement Recursion
def trim(s):
    if s[:1] != ' ' and s[-1:] != ' ':
        return s
    elif s[:1] == ' ':
        return trim(s[1:])
    else:
        return trim(s[:-1])

# Test:
if trim('hello  ') != 'hello':
    print('測試失敗!')
elif trim('  hello') != 'hello':
    print('測試失敗!')
elif trim('  hello  ') != 'hello':
    print('測試失敗!')
elif trim('  hello  world  ') != 'hello  world':
    print('測試失敗!')
elif trim('') != '':
    print('測試失敗!')
elif trim('    ') != '':
    print('測試失敗!')
else:
    print('測試成功!')