记录下os库中几个方法
os.curdir
The constant string used by the operating system to refer to the current directory. This is '.' for Windows and POSIX. Also available viaos.path
文档中原文如上，大致翻译如下：
常量字符串os.curdir被用来获取当前的目录。
os.sep
The character used by the operating system to separate pathname components. This is '/' for POSIX and '\\' for Windows. Note that knowing this is not sufficient to be able to parse or concatenate pathnames — use os.path.split() and os.path.join() — but it is occasionally useful. Also available via os.path
拼接路径中的符号
