1 >>> import os
2 >>> print("2:",os.path.join('/aaaa','/bbbb','/ccccc.txt'))
3 2: /ccccc.txt
5 >>> print("2:",os.path.join('/aaaa','/bbbb','ccccc.txt'))
6 2: /bbbb/ccccc.txt
7 >>> print("2:",os.path.join('/aaaa','bbbb','ccccc.txt'))
8 2: /aaaa/bbbb/ccccc.txt
9 >>> print("2:",os.path.join('/aaaa','/bbbb','ccccc.txt'))
10 2: /bbbb/ccccc.txt
11 >>> print("2:",os.path.join('/aaaa','/bbbb','/ccccc.txt'))
12 2: /ccccc.txt
13 >>> print("2:",os.path.join('aaaa','/bbbb','/ccccc.txt'))
14 2: /ccccc.txt
15 >>> print("2:",os.path.join('aaaa','/bbbb','ccccc.txt'))
16 2: /bbbb/ccccc.txt
17 >>> print("2:",os.path.join('aaaa','./bbbb','ccccc.txt'))
18 2: aaaa/./bbbb/ccccc.txt
结论：1.从最后添加的文件'ccccc.txt'开始看，出现第一个'/'时，添加path，'/'前面的所有都会被忽略。
2.要想第一个'/'前面的path也被添加，可以这样写'./'。
