The summary states it fine.  shutil.move happily overwrites read-
only files.

It looks like it indiscriminately catches OSError, and never bothers 
to check whether it's a permission error.

It'd be nice if permission errors raised an exception that was a 
subclass of OSError, then it'd be cake to fix this (at least for 
*nices; I'm not sure about the Windows implications).

According to tracker #810879, clobbering read-only files isn't the 
desired behavior for shutil.copyfile, so I doubt it's desired for 
shutil.move.

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Your analysis is not correct. On Unix, you need write
permission to the *directory* to rename. So the os.rename()
call simply succeeds on a read-only file if you have write
access to its parent directory. I think we could shield from
this by always using the fallback implementation
(copy2+unlink(src)), but I'm not sure what the implications
of that would be (qua performance and cross-platform issues).

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I don't think I will do anything about this anytime soon, so
unassigning myself.

Is this bug still relevant?

Here's a quick test:

Python 3.2a1+ (py3k:83811, Aug  8 2010, 09:00:22) 
[GCC 4.2.4 (Ubuntu 4.2.4-1ubuntu4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os, shutil
>>> open('a', 'w').write('a')
1
>>> open('b', 'w').write('b')
1
>>> os.chmod('b', 000)
>>> shutil.move('a', 'b')
>>> open('b').read()
'a'
>>> 

This is the correct behaviour on Unix, so I'd say this can be closed off.

Brian, Tim, any comments on this wrt Windows or do you think this can be closed?  Could there be an impact on any other OS?  I'll close if there's no response, unless someone else feels fit to close this anyway.

No reply to msg114985.

I haven't had time to investigate but it shouldn't be closed just yet. Someone will get to it.

I agree that this follows Unix behaviour: a read-only file is a file whose contents cannot be modified, but you can replace it with another totally different file. You can also delete it, by the way (*).

Also, even if this weren't the desired behaviour, changing it would break compatibility for existing scripts.

(*)

>>> open('b', 'w').write('b')
1
>>> os.chmod('b', 000)
>>> os.remove('b')
>>> open('b', 'r')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 2] No such file or directory: 'b'