How to use the portage.os.access function in portage

# EAPI (characters allowed in package names may vary).
			if not isvalidatom(newcp, eapi=mycpv.eapi):
				continue

			mynewcpv = mycpv.replace(mycpv_cp, str(newcp), 1)
			myoldpkg = catsplit(mycpv)[1]
			mynewpkg = catsplit(mynewcpv)[1]

			if (mynewpkg != myoldpkg) and os.path.exists(self.getname(mynewcpv)):
				writemsg(_("!!! Cannot update binary: Destination exists.\n"),
					noiselevel=-1)
				writemsg("!!! "+mycpv+" -> "+mynewcpv+"\n", noiselevel=-1)
				continue

			tbz2path = self.getname(mycpv)
			if os.path.exists(tbz2path) and not os.access(tbz2path,os.W_OK):
				writemsg(_("!!! Cannot update readonly binary: %s\n") % mycpv,
					noiselevel=-1)
				continue

			moves += 1
			mytbz2 = portage.xpak.tbz2(tbz2path)
			mydata = mytbz2.get_data()
			updated_items = update_dbentries([mylist], mydata, parent=mycpv)
			mydata.update(updated_items)
			mydata[b'PF'] = \
				_unicode_encode(mynewpkg + "\n",
				encoding=_encodings['repo.content'])
			mydata[b'CATEGORY'] = \
				_unicode_encode(mynewcat + "\n",
				encoding=_encodings['repo.content'])
			if mynewpkg != myoldpkg:

head, tail = os.path.split(mypath)
			if head in lib_dirs:
				libdir_contents_changed = True
				break
		if not libdir_contents_changed:
			makelinks = False

	if "CHOST" in settings and "CBUILD" in settings and \
		settings["CHOST"] != settings["CBUILD"]:
		ldconfig = find_binary("%s-ldconfig" % settings["CHOST"])
	else:
		ldconfig = os.path.join(eroot, "sbin", "ldconfig")

	if ldconfig is None:
		pass
	elif not (os.access(ldconfig, os.X_OK) and os.path.isfile(ldconfig)):
		ldconfig = None

	# Only run ldconfig as needed
	if makelinks and ldconfig:
		# ldconfig has very different behaviour between FreeBSD and Linux
		if ostype == "Linux" or ostype.lower().endswith("gnu"):
			# We can't update links if we haven't cleaned other versions first, as
			# an older package installed ON TOP of a newer version will cause ldconfig
			# to overwrite the symlinks we just made. -X means no links. After 'clean'
			# we can safely create links.
			writemsg_level(_(">>> Regenerating %setc/ld.so.cache...\n") % \
				(target_root,))
			os.system("cd / ; %s -X -r '%s'" % (ldconfig, target_root))
		elif ostype in ("FreeBSD", "DragonFly"):
			writemsg_level(_(">>> Regenerating %svar/run/ld-elf.so.hints...\n") % \
				target_root)

somewhere else.)
	
	"""

	# mycommand is either a str or a list
	if isinstance(mycommand, str):
		mycommand = mycommand.split()

	env = os.environ if env is None else env

	# If an absolute path to an executable file isn't given
	# search for it unless we've been told not to.
	binary = mycommand[0]
	if binary not in (BASH_BINARY, SANDBOX_BINARY, FAKEROOT_BINARY) and \
		(not os.path.isabs(binary) or not os.path.isfile(binary)
	    or not os.access(binary, os.X_OK)):
		binary = path_lookup and find_binary(binary) or None
		if not binary:
			raise CommandNotFound(mycommand[0])

	# If we haven't been told what file descriptors to use
	# default to propagating our stdin, stdout and stderr.
	if fd_pipes is None:
		fd_pipes = {
			0:portage._get_stdin().fileno(),
			1:sys.__stdout__.fileno(),
			2:sys.__stderr__.fileno(),
		}

	# mypids will hold the pids of all processes created.
	mypids = []

self.settings = settings
		self.logger = logger
		# Similar to emerge, sync needs a default umask so that created
		# files have sane permissions.
		os.umask(0o22)

		self.module_controller = portage.sync.module_controller
		self.module_names = self.module_controller.module_names
		self.hooks = {}
		for _dir in ["repo.postsync.d", "postsync.d"]:
			postsync_dir = os.path.join(self.settings["PORTAGE_CONFIGROOT"],
				portage.USER_CONFIG_PATH, _dir)
			hooks = OrderedDict()
			for filepath in util._recursive_file_list(postsync_dir):
				name = filepath.split(postsync_dir)[1].lstrip(os.sep)
				if os.access(filepath, os.X_OK):
					hooks[filepath] = name
				else:
					writemsg_level(" %s %s hook: '%s' is not executable\n"
						% (warn("*"), _dir, _unicode_decode(name),),
						level=logging.WARN, noiselevel=2)
			self.hooks[_dir] = hooks

def validate_cmd_var(v):
	"""
	Validate an evironment variable value to see if it
	contains an executable command as the first token.
	returns (valid, token_list) where 'valid' is boolean and 'token_list'
	is the (possibly empty) list of tokens split by shlex.
	"""
	invalid = False
	v_split = shlex_split(v)
	if not v_split:
		invalid = True
	elif os.path.isabs(v_split[0]):
		invalid = not os.access(v_split[0], os.EX_OK)
	elif find_binary(v_split[0]) is None:
		invalid = True
	return (not invalid, v_split)

def _check_world(self, onProgress):
		eroot = portage.settings['EROOT']
		self.world_file = os.path.join(eroot, portage.const.WORLD_FILE)
		self.found = os.access(self.world_file, os.R_OK)
		vardb = portage.db[eroot]["vartree"].dbapi

		from portage._sets import SETPREFIX
		sets = self._sets
		world_atoms = list(sets["selected"])
		maxval = len(world_atoms)
		if onProgress:
			onProgress(maxval, 0)
		for i, atom in enumerate(world_atoms):
			if not isinstance(atom, portage.dep.Atom):
				if atom.startswith(SETPREFIX):
					s = atom[len(SETPREFIX):]
					if s in sets:
						self.okay.append(atom)
					else:
						self.not_installed.append(atom)

return 1

	# as some people use a separate PORTAGE_TMPDIR mount
	# we prefer that as the checks below would otherwise be pointless
	# for those people.
	checkdir = first_existing(os.path.join(settings["PORTAGE_TMPDIR"], "portage"))

	if not os.access(checkdir, os.W_OK):
		writemsg(_("%s is not writable.\n"
			"Likely cause is that you've mounted it as readonly.\n") % checkdir,
			noiselevel=-1)
		return 1

	with tempfile.NamedTemporaryFile(prefix="exectest-", dir=checkdir) as fd:
		os.chmod(fd.name, 0o755)
		if not os.access(fd.name, os.X_OK):
			writemsg(_("Can not execute files in %s\n"
				"Likely cause is that you've mounted it with one of the\n"
				"following mount options: 'noexec', 'user', 'users'\n\n"
				"Please make sure that portage can execute files in this directory.\n") % checkdir,
				noiselevel=-1)
			return 1

	return os.EX_OK

def findLicensePath(self, license_name):
		for x in reversed(self.porttrees):
			license_path = os.path.join(x, "licenses", license_name)
			if os.access(license_path, os.R_OK):
				return license_path
		return None

def pickle_read(filename, default=None, debug=0):
	if not os.access(filename, os.R_OK):
		writemsg(_("pickle_read(): File not readable. '") + filename + "'\n", 1)
		return default
	data = None
	try:
		myf = open(_unicode_encode(filename,
			encoding=_encodings['fs'], errors='strict'), 'rb')
		mypickle = pickle.Unpickler(myf)
		data = mypickle.load()
		myf.close()
		del mypickle, myf
		writemsg(_("pickle_read(): Loaded pickle. '") + filename + "'\n", 1)
	except SystemExit as e:
		raise
	except Exception as e:
		writemsg(_("!!! Failed to load pickle: ") + str(e) + "\n", 1)
		data = default