How can I change the file permissions in Python?

Question

I am trying to find the equivalent Python code to this PHP code, but I'm not sure how to translate the 0640:

PHP code:

chmod($credentials_file, 0640);
chown($credentials_file, 'webapp');

I'm looking at the os.chmod documentation here, but I'm not sure how 0640 equates to stat.SOMETHING_HERE. Does anyone have any idea how to port these two lines to Python?

possible duplicate of [Python module os.chmod(file, 664) does not change the permission to rw-rw-r-- but -w--wx----](http://stackoverflow.com/questions/15607903/python-module-os-chmodfile-664-does-not-change-the-permission-to-rw-rw-r-bu) — Jay Blanchard, Feb 13 '15 at 16:35
That answer doesn't discuss the `stat.*` options though. How can I find what `0640` means so that I can use the approach that the docs (references in the question) recommend? — Brett, Feb 13 '15 at 16:37
`0640`: `6` = owner read/writable, `4` = group readable, `0` = others non-readable — Michael Berkowski, Feb 13 '15 at 16:39

jonrsharpe · Accepted Answer · 2015-02-13T16:54:16.960

0640 is an octal number (that is the meaning of the leading 0, which doesn't count as a digit), and means the following permissions (see e.g. Wikipedia):

the first digit is for the file's owner, and (as 6 is 110 in binary, where the bits are read, write and execute permission respectively) means read and write permission;
the second digit is for the group, and (as 4 is 100 in binary) means read-only; and
the third digit is for other users, and means no permissions (0 is 000!)

Therefore in this case you want to combine S_IRUSR (user read), S_IWUSR (user write) and S_IRGRP (group read):

>>> import stat
>>> oct(stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP)
'0640'

You can see each permission individually by displaying the octal number in binary form:

>>> bin(0640)
'0b110100000'

This breaks down as follows:

 # USR
0b 110 100 000
 # ^ user read (yes)
 #  ^ user write (yes)
 #   ^ user execute (no)

     # GRP
0b 110 100 000
     # ^ group read (yes)
     #  ^ group write (no)
     #   ^ group execute (no)

         # OTH
0b 110 100 000
         # ^ other read (no)
         #  ^ other write (no)
         #   ^ other execute (no)

Exactly what I needed to know (and not what the "possible duplicate" post talks about). Thanks! — Brett, Feb 13 '15 at 16:39
@Brett I've just realised I didn't make explicit that you *can* just use `0640` as the second argument to `os.chmod`; the constants in `stat` are just e.g. `stat.S_IWUSR == 128`, there's nothing special about them. — jonrsharpe, Feb 13 '15 at 18:30

How can I change the file permissions in Python?

1 Answers1