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confusion with os.chmod() and follow_symlinks


On Fri, Feb 22, 2019 at 09:21:07PM +0100, Karsten Hilbert wrote:

> Am I confused ?
> 
> 	ncq at hermes:~$ python3
> 	Python 3.7.2+ (default, Feb  2 2019, 14:31:48)
> 	[GCC 8.2.0] on linux
> 	Type "help", "copyright", "credits" or "license" for more information.
> 	>>> import os
> 	>>> print(os.supports_follow_symlinks)
> 	{<built-in function utime>, <built-in function chown>, <built-in function access>, <built-in function stat>, <built-in function link>}
> 	>>> os.chmod in os.supports_follow_symlinks
> 	False
> 	>>> os.chmod('/tmp/test', 0o0700, follow_symlinks = False)
> 	Traceback (most recent call last):
> 	  File "<stdin>", line 1, in <module>
> 	NotImplementedError: chmod: follow_symlinks unavailable on this platform
> 	>>>
> 
> I would only have expected this exception when I actually
> request the unavailable functionality, like so:
> 
> 	os.chmod('/tmp/test', 0o0700, follow_symlinks = True)
> 
> This, however, works:
> 
> 		os.chmod('/tmp/test', 0o0700)
> 
> DESPITE the documentation saying
> 
> 	os.chmod(path, mode, *, dir_fd=None, follow_symlinks=True)
> 
> IOW, the default for <follow_symlinks> being "True", which is
> certainly illogical to succeed when it is not even supported
> on this platform.

Because, naively, I'd have assumed this to work:

	os.chmod(directory, mode, follow_symlinks = (os.chmod in os.supports_follow_symlinks))

Karsten
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