Python module os.chmod(file, 664) does not change the permission to rw-rw-r-- but -w--wx----

Question

Recently I am using Python module os, when I tried to change the permission of a file, I did not get the expected result. For example, I intended to change the permission to rw-rw-r--,

os.chmod("/tmp/test_file", 664)

The ownership permission is actually -w--wx--- (230)

--w--wx--- 1 ag ag 0 Mar 25 05:45 test_file

However, if I change 664 to 0664 in the code, the result is just what I need, e.g.

os.chmod("/tmp/test_file", 0664)

The result is:

-rw-rw-r-- 1 ag ag 0 Mar 25 05:55 test_file

Could anybody help explaining why does that leading 0 is so important to get the correct result?

Answer 1

Found this on a different forum

If you're wondering why that leading zero is important, it's because permissions are set as an octal integer, and Python automagically treats any integer with a leading zero as octal. So os.chmod("file", 484) (in decimal) would give the same result.

What you are doing is passing 664 which in octal is 1230

In your case you would need

os.chmod("/tmp/test_file", 436)

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[Update] Note, for Python 3 you have prefix with 0o (zero oh). E.G, 0o666