如何在Python中更改文件权限？

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?

Answer 1

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)