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August 16, 2016 13:27
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Symbolic chmod in Python
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| # Found on https://www.daniweb.com/programming/software-development/code/243659/change-file-permissions-symbolically-linux | |
| """ module chmodsym.py (linux) | |
| This module defines a function chmod(location, description) | |
| which allows to change a file's permission with a symbolic | |
| description of the mode, similar to the shell command 'chmod'. | |
| Tested with python 2.6 and 3.1. | |
| """ | |
| import os, stat | |
| import functools | |
| import operator | |
| def chmod(location, description): | |
| """chmod(location, description) --> None | |
| Change the access permissions of file, using a symbolic description | |
| of the mode, similar to the format of the shell command chmod. | |
| The format of description is | |
| * an optional letter in o, g, u, a (no letter means a) | |
| * an operator in +, -, = | |
| * a sequence of letters in r, w, x, or a single letter in o, g, u | |
| Example: | |
| chmod(myfile, "u+x") # make the file executable for it's owner. | |
| chmod(myfile, "o-rwx") # remove all permissions for all users not in the group. | |
| See also the man page of chmod. | |
| """ | |
| if chmod.regex is None: | |
| import re | |
| chmod.regex = re.compile(r"(?P<who>[uoga]?)(?P<op>[+\-=])(?P<value>[ugo]|[rwx]*)") | |
| mo = chmod.regex.match(description) | |
| who, op, value = mo.group("who"), mo.group("op"), mo.group("value") | |
| if not who: | |
| who = "a" | |
| mode = os.stat(location)[stat.ST_MODE] | |
| if value in ("o", "g", "u"): | |
| mask = ors((stat_bit(who, z) for z in "rwx" if (mode & stat_bit(value, z)))) | |
| else: | |
| mask = ors((stat_bit(who, z) for z in value)) | |
| if op == "=": | |
| mode &= ~ ors((stat_bit(who, z) for z in "rwx")) | |
| mode = (mode & ~mask) if (op == "-") else (mode | mask) | |
| os.chmod(location, mode) | |
| chmod.regex = None | |
| # Helper functions | |
| def stat_bit(who, letter): | |
| if who == "a": | |
| return stat_bit("o", letter) | stat_bit("g", letter) | stat_bit("u", letter) | |
| return getattr(stat, "S_I%s%s" % (letter.upper(), stat_bit.prefix[who])) | |
| stat_bit.prefix = dict(u = "USR", g = "GRP", o = "OTH") | |
| def ors(sequence, initial = 0): | |
| return functools.reduce(operator.__or__, sequence, initial) | |
| # Test code | |
| def test_code(): | |
| import subprocess as sp | |
| def touch(location): | |
| sp.Popen("touch %s" % location, shell=True).wait() | |
| def get_mode_by_ls(location): | |
| """Run ls and return a string like '-r--r--r-' giving the mode.""" | |
| popen = sp.Popen(["ls", "-l", location], stdout=sp.PIPE) | |
| sout, serr = popen.communicate() | |
| return sout[:10] |
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