[python] Changing file permission in Python

I am trying to change permission of a file access:

os.chmod(path, mode)

I want to make it read-only:

os.chmod(path, 0444)

Is there any other way make a file read-only?

FYI here is a function to convert a permission string with 9 characters (e.g. 'rwsr-x-wt') to a mask that can be used with os.chmod().

def perm2mask(p):
        
    assert len(p) == 9, 'Bad permission length'
    assert all(p[k] in 'rw-' for k in [0,1,3,4,6,7]), 'Bad permission format (read-write)'
    assert all(p[k] in 'xs-' for k in [2,5]), 'Bad permission format (execute)'
    assert p[8] in 'xt-', 'Bad permission format (execute other)'
    
    m = 0
    
    if p[0] == 'r': m |= stat.S_IRUSR 
    if p[1] == 'w': m |= stat.S_IWUSR 
    if p[2] == 'x': m |= stat.S_IXUSR 
    if p[2] == 's': m |= stat.S_IXUSR | stat.S_ISUID 
    
    if p[3] == 'r': m |= stat.S_IRGRP 
    if p[4] == 'w': m |= stat.S_IWGRP 
    if p[5] == 'x': m |= stat.S_IXGRP 
    if p[5] == 's': m |= stat.S_IXGRP | stat.S_ISGID 
    
    if p[6] == 'r': m |= stat.S_IROTH 
    if p[7] == 'w': m |= stat.S_IWOTH 
    if p[8] == 'x': m |= stat.S_IXOTH 
    if p[8] == 't': m |= stat.S_IXOTH | stat.S_ISVTX
    
    return m

Note that setting SUID/SGID/SVTX bits will automatically set the corresponding execute bit. Without this, the resulting permission would be invalid (ST characters).

All the current answers clobber the non-writing permissions: they make the file readable-but-not-executable for everybody. Granted, this is because the initial question asked for 444 permissions -- but we can do better!

Here's a solution that leaves all the individual "read" and "execute" bits untouched. I wrote verbose code to make it easy to understand; you can make it more terse if you like.

import os
import stat

def remove_write_permissions(path):
    """Remove write permissions from this path, while keeping all other permissions intact.

    Params:
        path:  The path whose permissions to alter.
    """
    NO_USER_WRITING = ~stat.S_IWUSR
    NO_GROUP_WRITING = ~stat.S_IWGRP
    NO_OTHER_WRITING = ~stat.S_IWOTH
    NO_WRITING = NO_USER_WRITING & NO_GROUP_WRITING & NO_OTHER_WRITING

    current_permissions = stat.S_IMODE(os.lstat(path).st_mode)
    os.chmod(path, current_permissions & NO_WRITING)

Why does this work?

As John La Rooy pointed out,stat.S_IWUSR basically means "the bitmask for the user's write permissions". We want to set the corresponding permission bit to 0. To do that, we need the exact opposite bitmask (i.e., one with a 0 in that location, and 1's everywhere else). The ~ operator, which flips all the bits, gives us exactly that. If we apply this to any variable via the "bitwise and" operator (&), it will zero out the corresponding bit.

We need to repeat this logic with the "group" and "other" permission bits, too. Here we can save some time by just &'ing them all together (forming the NO_WRITING bit constant).

The last step is to get the current file's permissions, and actually perform the bitwise-and operation.

os.chmod(path, 0444) is the Python command for changing file permissions in Python 2.x. For a combined Python 2 and Python 3 solution, change 0444 to 0o444.

You could always use Python to call the chmod command using subprocess. I think this will only work on Linux though.

import subprocess

subprocess.call(['chmod', '0444', 'path'])

os.chmod(path, stat.S_IRUSR | stat.S_IRGRP | stat.S_IROTH)

stat

The following flags can also be used in the mode argument of os.chmod():

stat.S_ISUID Set UID bit.

stat.S_ISGID Set-group-ID bit. This bit has several special uses. For a directory it indicates that BSD semantics is to be used for that directory: files created there inherit their group ID from the directory, not from the effective group ID of the creating process, and directories created there will also get the S_ISGID bit set. For a file that does not have the group execution bit (S_IXGRP) set, the set-group-ID bit indicates mandatory file/record locking (see also S_ENFMT).

stat.S_ISVTX Sticky bit. When this bit is set on a directory it means that a file in that directory can be renamed or deleted only by the owner of the file, by the owner of the directory, or by a privileged process.

stat.S_IRWXU Mask for file owner permissions.

stat.S_IRUSR Owner has read permission.

stat.S_IWUSR Owner has write permission.

stat.S_IXUSR Owner has execute permission.

stat.S_IRWXG Mask for group permissions.

stat.S_IRGRP Group has read permission.

stat.S_IWGRP Group has write permission.

stat.S_IXGRP Group has execute permission.

stat.S_IRWXO Mask for permissions for others (not in group).

stat.S_IROTH Others have read permission.

stat.S_IWOTH Others have write permission.

stat.S_IXOTH Others have execute permission.

stat.S_ENFMT System V file locking enforcement. This flag is shared with S_ISGID: file/record locking is enforced on files that do not have the group execution bit (S_IXGRP) set.

stat.S_IREAD Unix V7 synonym for S_IRUSR.

stat.S_IWRITE Unix V7 synonym for S_IWUSR.

stat.S_IEXEC Unix V7 synonym for S_IXUSR.

Just add 0 before the permission number:
For example - we want to give all permissions - 777
Syntax: os.chmod("file_name" , permission)

import os
os.chmod("file_name" , 0777)

Python version 3.7 does not support this syntax. It requires '0o' prefix for octal literals - this is the comment I have got in PyCharm

So for python 3.7, it will be

import os
os.chmod("file_name" , 0o777)

Simply include permissions integer in octal (works for both python 2 and python3):

os.chmod(path, 0o444)

You can use, pathlib also

from pathlib import Path

fl = Path("file_name")

fl.chmod(0o444)

No need to remember flags. Remember that you can always do:

subprocess.call(["chmod", "a-w", "file/path])

Not portable but easy to write and remember:

• u - user
• g - group
• o - other
• a - all
• + or - (add or remove permission)
• r - read
• w - write
• x - execute

Refer man chmod for additional options and more detailed explanation.