1. Windows

倒斜杠有两个，因为每个倒斜杠需要由另一个倒斜杠字符来转义。

Microsoft Windows [版本 6.1.7601]
版权所有 (c) 2009 Microsoft Corporation。保留所有权利。C:\Users\foreverstrong>python
Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 08:06:12) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.path.join("usr", "include", "c++")
'usr\\include\\c++'
>>>
>>> print(os.path.join("usr", "include", "c++"))
usr\include\c++
>>>
>>>
>>> files = ["a.txt", "b.txt", "c.txt"]
>>> for filename in files:
...     print(os.path.join("C:\\Users\\Default", filename))
...
C:\Users\Default\a.txt
C:\Users\Default\b.txt
C:\Users\Default\c.txt
>>>

2. Linux

​​​

strong@foreverstrong:~$ python
Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.path.join("usr", "include", "c++")
'usr/include/c++'
>>> 
>>> print(os.path.join("usr", "include", "c++"))
usr/include/c++
>>> 
>>> 
>>> files = ["a.txt", "b.txt", "c.txt"]
>>> for filename in files:
...     print(os.path.join("/Users/Default", filename))
... 
/Users/Default/a.txt
/Users/Default/b.txt
/Users/Default/c.txt
>>> 
>>> 
>>> files = ["a.txt", "b.txt", "c.txt"]
>>> for filename in files:
...     print(os.path.join("/Users/Default/", filename))
... 
/Users/Default/a.txt
/Users/Default/b.txt
/Users/Default/c.txt
>>> 
>>> 
>>> files = ["a.txt", "b.txt", "c.txt"]
>>> for filename in files:
...     print(os.path.join("/Users/Default//", filename))
... 
/Users/Default//a.txt
/Users/Default//b.txt
/Users/Default//c.txt
>>> 
>>> 
>>> files = ["a.txt", "b.txt", "c.txt"]
>>> for filename in files:
...     print(os.path.join("/Users/Default///", filename))
... 
/Users/Default///a.txt
/Users/Default///b.txt
/Users/Default///c.txt
>>> 

References

[1] Yongqiang Cheng, https://yongqiang.blog.csdn.net/
[2] Windows 和 Linux 系统正斜杠 (斜杠 /) 和反斜杠 (倒斜杠 ), https://yongqiang.blog.csdn.net/article/details/106111070