file permissions on windows XP (home)

[Duncan Booth]

Peter Hansen wrote:

>> 
>> Why is python returing True from os.access?
>> Why isn't chmod doing anything?
> 
> Check your results using os.stat() after doing that, perhaps?  If it 
> shows the right values for the permissions, then clearly the problem has 
> nothing to do with Python per se, or your own code.
> 

And also remember that in windows the mode in os.chmod and os.stat is only 
loosely related to the actual permissions on the file. In particular there 
is a 'readonly' flag which is separate from whether any particular user 
or group has write access. The only way to tell whether you have access to 
a file in windows really is to try to open it and handle the exception.

Try using the properties panel, or the windows CACLS to display the 
security permissions on the file.

If you start with a plain file, then you and administrators probably have 
full access (CACLS will display 'your username:F'). If you use Python to 
set an access mode, it simply tries to toggle the attributes on the file 
itself. If you use Cygwin's chmod it will mess about with the security 
permissions in an attempt to get as close to the Unix file mode as it can, 
so your nice simple 'F' mode might become something truly horrendous:

Before:
C:\temp>cacls testfile.txt
C:\temp\testfile.txt BUILTIN\Administrators:F
                     NT AUTHORITY\SYSTEM:F
                     DELL5150\Duncan:F
                     BUILTIN\Users:R

C:\temp>\cygwin\bin\chmod 744 testfile.txt

C:\temp>cacls testfile.txt
C:\temp\testfile.txt DELL5150\Duncan:(special access:)
                                     STANDARD_RIGHTS_ALL
                                     DELETE
                                     READ_CONTROL
                                     WRITE_DAC
                                     WRITE_OWNER
                                     SYNCHRONIZE
                                     STANDARD_RIGHTS_REQUIRED
                                     FILE_GENERIC_READ
                                     FILE_GENERIC_WRITE
                                     FILE_GENERIC_EXECUTE
                                     FILE_READ_DATA
                                     FILE_WRITE_DATA
                                     FILE_APPEND_DATA
                                     FILE_READ_EA
                                     FILE_WRITE_EA
                                     FILE_EXECUTE
                                     FILE_READ_ATTRIBUTES
                                     FILE_WRITE_ATTRIBUTES

                     DELL5150\None:(special access:)
                                   READ_CONTROL
                                   SYNCHRONIZE
                                   FILE_GENERIC_READ
                                   FILE_READ_DATA
                                   FILE_READ_EA
                                   FILE_READ_ATTRIBUTES

                     Everyone:(special access:)
                              READ_CONTROL
                              SYNCHRONIZE
                              FILE_GENERIC_READ
                              FILE_READ_DATA
                              FILE_READ_EA
                              FILE_READ_ATTRIBUTES

                     BUILTIN\Administrators:F
                     NT AUTHORITY\SYSTEM:F
                     BUILTIN\Users:R