python中的路径拼接问题

def test2():
    s1, s2, s3 = 'home', 'courses', 'test'
    res = os.path.join(s1, s2, s3)
    print(res)  # home\courses\test
    s2 = '/courses'
    res = os.path.join(s1, s2, s3)
    print(res)  # /courses\test
    s1, s2, s3 = '\home', 'courses', 'test'
    res = os.path.join(s1, s2, s3)
    print(res)  # \home\courses\test
    s1, s2, s3 = '\home', 'courses', ''
    res = os.path.join(s1, s2, s3)
    print(res)  #\home\courses\

ss = 'E:\\Cloud\\20200813105812L\\res\\1\\425'
a = '\\8_live_1962854245_export_files\\media'

c = os.path.join(ss,a)
print(c)

print("0:",os.path.join('\\aaaa','bbbb','ccccc.txt'))
print("0:",os.path.join('aaaa','\\bbbb','ccccc.txt'))
print("0:",os.path.join('aaaa','bbbb','\\ccccc.txt'))
print("0:",os.path.join('aaaa','\\bbbb','\\ccccc.txt'))
print("0:",os.path.join('aaaa','/bbbb','\\ccccc.txt'))
print("0:",os.path.join('aaaa','/bbbb','/ccccc.txt'))

结果：
0: \aaaa\bbbb\ccccc.txt
0: \bbbb\ccccc.txt
0: \ccccc.txt
0: \ccccc.txt	
0: \ccccc.txt
0: /ccccc.txt

print("1:",os.path.join('aaaa','xxxxxx','./bbb','ccccc.txt'))
print("1:",os.path.join('./aaaa','xxxxxx','./bbb','./ccccc.txt'))

结果：
1: aaaa\xxxxxx\./bbb\ccccc.txt
1: ./aaaa\xxxxxx\./bbb\./ccccc.txt

# 后面的斜杠反斜杠
print("1:",os.path.join('c:','bbb'))
print("1:",os.path.join('c:','bbb/\\','ccccc.txt'))

# 未加盘符
print("2:",os.path.join('c','/bbb','ccccc.txt')) # 会以/bbb开头
print("2:",os.path.join('c:','/bbb','ccccc.txt')) # 虽然有反斜杆 但是依旧以C：开头
print("2:",os.path.join('c:/','/bbb','ccccc.txt')) # 多个/只会有一个

# 盘符后面未加斜杠
print("3:",os.path.join('c:','bbb','ccccc.txt'))
print("3:",os.path.join('c:/','bbb','ccccc.txt'))

结果:
1: c:bbb
1: c:bbb/\ccccc.txt
2: /bbb\ccccc.txt
2: c:/bbb\ccccc.txt
2: c:/bbb\ccccc.txt
3: c:bbb\ccccc.txt
3: c:/bbb\ccccc.txt