[issue37686] No error message in joining two root directories

[Bin Hu]

New submission from Bin Hu <hubin.lanl at gmail.com>:

Two root directories shall not be joined in the first place. But, when such a command is passed, os.path.join() module should give a warning message instead of just keeping the second argument being passed as the output. 

Python 3.7.3 (default, Mar 27 2019, 16:54:48)
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IPython 7.4.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: from os import path

In [2]: a = '/tmp'

In [3]: b = '/data'

In [4]: print(path.join(a, b))
/data

In [5]: b = 'data'

In [6]: print(path.join(a, b))
/tmp/data

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components: Extension Modules
messages: 348457
nosy: Bin Hu
priority: normal
severity: normal
status: open
title: No error message in joining two root directories
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37686>
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