How to use the portage.os.path.exists function in portage

def _start(self):

		vardb = self.pkg.root_config.trees["vartree"].dbapi
		dbdir = vardb.getpath(self.pkg.cpv)
		if not os.path.exists(dbdir):
			# Apparently the package got uninstalled
			# already, so we can safely return early.
			self.returncode = os.EX_OK
			self._async_wait()
			return

		self.settings.setcpv(self.pkg)
		cat, pf = portage.catsplit(self.pkg.cpv)
		myebuildpath = os.path.join(dbdir, pf + ".ebuild")

		try:
			portage.doebuild_environment(myebuildpath, "prerm",
				settings=self.settings, db=vardb)
		except UnsupportedAPIException:
			# This is safe to ignore since this function is
			# guaranteed to set PORTAGE_BUILDDIR even though

yield self._build_dir.async_lock()
			else:
				self.settings.pop('PORTAGE_IPC_DAEMON', None)
		else:
			# Since the IPC daemon is disabled, use a simple tempfile based
			# approach to detect unexpected exit like in bug #190128.
			self.settings.pop('PORTAGE_IPC_DAEMON', None)
			if self.phase not in self._phases_without_builddir:
				exit_file = os.path.join(
					self.settings['PORTAGE_BUILDDIR'],
					'.exit_status')
				self.settings['PORTAGE_EBUILD_EXIT_FILE'] = exit_file
				try:
					os.unlink(exit_file)
				except OSError:
					if os.path.exists(exit_file):
						# make sure it doesn't exist
						raise
			else:
				self.settings.pop('PORTAGE_EBUILD_EXIT_FILE', None)

		if start_ipc_daemon:
			self.settings['PORTAGE_IPC_DAEMON'] = "1"
			self._start_ipc_daemon()

		if self.fd_pipes is None:
			self.fd_pipes = {}
		null_fd = None
		if 0 not in self.fd_pipes and \
			self.phase not in self._phases_interactive_whitelist and \
			"interactive" not in self.settings.get("PROPERTIES", "").split():
			null_fd = os.open('/dev/null', os.O_RDONLY)

def action_metadata(settings, portdb, myopts, porttrees=None):
	if porttrees is None:
		porttrees = portdb.porttrees
	portage.writemsg_stdout("\n>>> Updating Portage cache\n")
	cachedir = os.path.normpath(settings.depcachedir)
	if cachedir in ["/",    "/bin", "/dev",  "/etc",  "/home",
					"/lib", "/opt", "/proc", "/root", "/sbin",
					"/sys", "/tmp", "/usr",  "/var"]:
		print("!!! PORTAGE_DEPCACHEDIR IS SET TO A PRIMARY " + \
			"ROOT DIRECTORY ON YOUR SYSTEM.", file=sys.stderr)
		print("!!! This is ALMOST CERTAINLY NOT what you want: '%s'" % cachedir, file=sys.stderr)
		sys.exit(73)
	if not os.path.exists(cachedir):
		os.makedirs(cachedir)

	auxdbkeys = portdb._known_keys

	class TreeData:
		__slots__ = ('dest_db', 'eclass_db', 'path', 'src_db', 'valid_nodes')
		def __init__(self, dest_db, eclass_db, path, src_db):
			self.dest_db = dest_db
			self.eclass_db = eclass_db
			self.path = path
			self.src_db = src_db
			self.valid_nodes = set()

	porttrees_data = []
	for path in porttrees:
		src_db = portdb._pregen_auxdb.get(path)

slot = self.settings.get(var_name, '')
					if not slot.strip():
						showMessage(_("!!! SLOT is undefined\n"),
							level=logging.ERROR, noiselevel=-1)
						return 1
					write_atomic(os.path.join(inforoot, var_name), slot + '\n')

			if val != self.settings.get(var_name, ''):
				self._eqawarn('preinst',
					[_("QA Notice: Expected %(var_name)s='%(expected_value)s', got '%(actual_value)s'\n") % \
					{"var_name":var_name, "expected_value":self.settings.get(var_name, ''), "actual_value":val}])

		def eerror(lines):
			self._eerror("preinst", lines)

		if not os.path.exists(self.dbcatdir):
			ensure_dirs(self.dbcatdir)

		otherversions = []
		for v in self.vartree.dbapi.cp_list(self.mysplit[0]):
			otherversions.append(v.split("/")[1])

		cp = self.mysplit[0]
		slot_atom = "%s:%s" % (cp, slot)

		# filter any old-style virtual matches
		slot_matches = [cpv for cpv in self.vartree.dbapi.match(slot_atom) \
			if cpv_getkey(cpv) == cp]

		if self.mycpv not in slot_matches and \
			self.vartree.dbapi.cpv_exists(self.mycpv):
			# handle multislot or unapplied slotmove

apply_secpass_permissions(download_path,
								gid=portage_gid, mode=0o664, mask=0o2)
						except FileNotFound:
							pass
						except PortageException as e:
							if not os.access(download_path, os.R_OK):
								writemsg(_("!!! Failed to adjust permissions:"
									" %s\n") % str(e), noiselevel=-1)
							del e

					# If the file is empty then it's obviously invalid.  Don't
					# trust the return value from the fetcher.  Remove the
					# empty file and try to download again.
					try:
						mystat = os.lstat(download_path)
						if mystat.st_size == 0 or (stat.S_ISLNK(mystat.st_mode) and not os.path.exists(download_path)):
							os.unlink(download_path)
							fetched = 0
							continue
					except EnvironmentError:
						pass

					if mydigests is not None and myfile in mydigests:
						try:
							mystat = os.stat(download_path)
						except OSError as e:
							if e.errno not in (errno.ENOENT, errno.ESTALE):
								raise
							del e
							fetched = 0
						else:

def _open_shelve(self, db_file, db_desc):
		if self.options.dry_run:
			open_flag = "r"
		else:
			open_flag = "c"

		if self.options.dry_run and not os.path.exists(db_file):
			db = {}
		else:
			try:
				db = shelve.open(db_file, flag=open_flag)
			except ImportError as e:
				# ImportError has different attributes for python2 vs. python3
				if (getattr(e, 'name', None) == 'bsddb' or
					getattr(e, 'message', None) == 'No module named bsddb'):
					from bsddb3 import dbshelve
					db = dbshelve.open(db_file, flags=open_flag)

		if self.options.dry_run:
			logging.warning("dry-run: %s db opened in readonly mode" % db_desc)
			if not isinstance(db, dict):
				volatile_db = dict((k, db[k]) for k in db)
				db.close()

'''
		retvcs = []
		pathprep = cwd

		while depth is None or depth > 0:
			for vcs_type in _FindVCS_data:
				vcs_dir = os.path.join(pathprep, vcs_type.dir_name)
				if os.path.isdir(vcs_dir):
					logging.debug(
						'FindVCS: found %(name)s dir: %(vcs_dir)s' % {
							'name': vcs_type.name,
							'vcs_dir': os.path.abspath(vcs_dir)})
					retvcs.append(vcs_type.name)
				elif vcs_type.file_name:
					vcs_file = os.path.join(pathprep, vcs_type.file_name)
					if os.path.exists(vcs_file):
						logging.debug(
							'FindVCS: found %(name)s file: %(vcs_file)s' % {
								'name': vcs_type.name,
								'vcs_file': os.path.abspath(vcs_file)})
						retvcs.append(vcs_type.name)

			if retvcs:
				break
			pathprep = os.path.join(pathprep, '..')
			if os.path.realpath(pathprep).strip('/') == '':
				break
			if depth is not None:
				depth = depth - 1

		return retvcs

def new(self, **kwargs):
		if kwargs:
			self._kwargs(kwargs)
		try:
			if not os.path.exists(self.repo.location):
				os.makedirs(self.repo.location)
				self.logger(self.self.xterm_titles,
					'Created New Directory %s ' % self.repo.location )
		except IOError:
			return (1, False)
		return self.update()

def _remove_failed_dirs(self, failed_pkgs):
		"""
		Remove the directories of packages that failed to merge.

		@param failed_pkgs: failed packages whose directories to remove
		@type failed_pkg: dict
		"""
		for failed_pkg in failed_pkgs:
			pkg_path = os.path.join(self._vardb_path, failed_pkg)
			# delete failed merge directory if it exists (it might not exist
			# if loaded from tracking file)
			if os.path.exists(pkg_path):
				shutil.rmtree(pkg_path)
			# TODO: try removing package CONTENTS to prevent orphaned

def exists(self, **kwargs):
		'''Tests whether the repo actually exists'''
		return os.path.exists(os.path.join(self.repo.location, '.svn'))