Basic python chmod for windows

A basic python version of chmod for Windows using pywin32:

import ntsecuritycon
import win32security

DACL_PRESENT = 1
DACL_DEFAULT = 0

def WinChmod(filename, acl_list, user="SYSTEM"):
  """Provide chmod-like functionality for windows.

  Doco links:
    goo.gl/n7YR1
    goo.gl/rDv81
    goo.gl/hDobb

  Args:
    filename: target filename for acl
    acl_list: list of ntsecuritycon acl strings to be applied with bitwise OR.
              e.g. ["FILE_GENERIC_READ", "FILE_GENERIC_WRITE"]
    user: username string
  Raises:
    AttributeError: if a bad permission is passed
    RuntimeError: if filename doesn't exist
  """
  if not os.path.exists(filename):
    raise RuntimeError("filename %s does not exist" % filename)

  acl_bitmask = int()
  for acl in acl_list:
    acl_bitmask |= getattr(ntsecuritycon, acl)

  dacl = win32security.ACL()
  win_user, _, _ = win32security.LookupAccountName("", user)

  dacl.AddAccessAllowedAce(win32security.ACL_REVISION,
                           acl_bitmask, win_user)

  security_descriptor = win32security.GetFileSecurity(
      filename, win32security.DACL_SECURITY_INFORMATION)

  # Tell windows to set the acl and mark it as explicitly set
  security_descriptor.SetSecurityDescriptorDacl(DACL_PRESENT, dacl,
                                                DACL_DEFAULT)
  win32security.SetFileSecurity(filename,
                                win32security.DACL_SECURITY_INFORMATION,
                                security_descriptor)