【Python3笔记】关于os.path.isabs()

先来看几个使用os,path.isabs()的例子：

很显然，第一个路径是没有问题，而后面都是我随便输入的一串字符，为什么有的返回true有的返回false呢？

 

我查看了python3.5的文档，发现了这样一句话：

os.path.isabs(path)

return true if path is an absolute pathname. on unix, that means it begins with a slash, on windows that it begins with a (back)slash after chopping off a potential drive letter.

也就是说在window系统下，如果输入的字符串以" / "开头，os.path.isabs()就会返回true，那么第四个例子就可以理解了。

 

而第二个和第三个有什么区别呢？不是都应该返回false吗？

查阅资料后我找到了下面这段话：

the current os.path.isabs documentation says:
> isabs(path) 
>    return true if path is an absolute pathname (begins with a slash). 
the "begins with a slash" part is incorrect since certain systems use a
different pathname notation.
for example, on macintosh (where os.sep == ":") this is an absolute
pathname:
harddrivename:foldername1:foldername2:filename.ext
...and this is a relative one:
:foldername1:filename.ext
moreover, on windows os.path.isabs('\\') returns true since '\\' is an
alias for the current drive letter (e.g. c:\\) hence, independently from
what said before, the documentation should include also the "backslash"
term.
it turns out that on windows there are really 4 different kinds of paths:
1) completely relative, e.g. foo\bar
2) completely absolute, e.g. c:\foo\bar or \\server\share
3) halfbreeds with no drive, e.g. \foo\bar
4) halfbreeds relative to the current working directory on a specific drive, e.g. c:foo\bar
python 2.5's os.path.isabs() method considers both (2) and (3) to be absolute;

虽然是python2的，但是这和python3应该没什么区别。从上面这段话可以知道，在windows系统上，以“  //  "开头的字符串，os.path.isabs也会返回true。

然后我们又可以知道：

这就能解释为什么第二个返回false而第三个返回true了。