[gentoo-commits] portage r10814 - in main/branches/prefix: cnf pym/_emerge pym/portage pym/portage/cache pym/portage/dbapi

[Fabian Groffen (grobian)]

Author: grobian
Date: 2008-06-27 14:47:19 +0000 (Fri, 27 Jun 2008)
New Revision: 10814

Modified:
   main/branches/prefix/cnf/sets.conf
   main/branches/prefix/pym/_emerge/__init__.py
   main/branches/prefix/pym/portage/__init__.py
   main/branches/prefix/pym/portage/cache/mappings.py
   main/branches/prefix/pym/portage/dbapi/bintree.py
   main/branches/prefix/pym/portage/dbapi/porttree.py
   main/branches/prefix/pym/portage/getbinpkg.py
   main/branches/prefix/pym/portage/util.py
Log:
   Merged from trunk 10788:10801

   | 10789   | Swap out the whole Package.root_config attribute inside      |
   | zmedico | depgraph.break_refs().                                       |
   
   | 10790   | Add a generic portage.cache.mappings.slot_dict_class()       |
   | zmedico | function which generates mapping classes that behave similar |
   |         | to a dict but store values as object attributes that are     |
   |         | allocated via __slots__. Instances of these objects have a   |
   |         | smaller memory footprint than a normal dict object. These    |
   |         | classes are used to reduce the memory footprint of the       |
   |         | dbapi.aux_get() caches and the Package.metadata attribute.   |
   
   | 10791   | Fix indentation.                                             |
   | zmedico |                                                              |
   
   | 10792   | Fix KeyError constructor style.                              |
   | zmedico |                                                              |
   
   | 10793   | Fix typo.                                                    |
   | zmedico |                                                              |
   
   | 10794   | Add docstring to slot_dict_class().                          |
   | zmedico |                                                              |
   
   | 10795   | Fix typo.                                                    |
   | zmedico |                                                              |
   
   | 10796   | Use SlotDict where appropriate in binarytree._populate().    |
   | zmedico |                                                              |
   
   | 10797   | Make PackageIndex use SlotDict for package metadata storage. |
   | zmedico | The set of allowed keys is passed into the PackageIndex      |
   |         | constructor (normal dict instances will be used if the set   |
   |         | of keys is not passed in for some reason). A                 |
   |         | SlotDict.allowed_keys attribute now provides access to a     |
   |         | frozenset of allowed keys.                                   |
   
   | 10798   | Implement lazy initialization of global "portdb", "settings" |
   | zmedico | and other variables that pollute the portage module. This    |
   |         | works by initializing the global variables with dummy        |
   |         | "proxy" objects that serve as a means to trigger lazy        |
   |         | initialization. As soon as the first attribute access or     |
   |         | method call occurs on one of the proxy objects, it causes    |
   |         | all the proxy objects to be replaced with the real ones.     |
   |         | It's possible for an unsupported attribute access or method  |
   |         | call on a proxy object to trigger an error, leading to       |
   |         | breakage. However, hopefully these such corner cases will    |
   |         | negligible (only time will tell).                            |
   
   | 10799   | Use a separate proxy type to trigger portage.portdb          |
   | zmedico | initialization separately from the rest of the legacy global |
   |         | variables. This can be useful since sometimes the other      |
   |         | variables are needed while the portdb is not.                |
   
   | 10800   | Also use a separate proxy type for portage.mtimedb since     |
   | zmedico | it's independent from the portdb and settings.               |
   
   | 10801   | change default name of EverythingSet to @all-installed (bug  |
   | genone  | #229467)                                                     |


Modified: main/branches/prefix/cnf/sets.conf
===================================================================
--- main/branches/prefix/cnf/sets.conf	2008-06-27 12:11:33 UTC (rev 10813)
+++ main/branches/prefix/cnf/sets.conf	2008-06-27 14:47:19 UTC (rev 10814)
@@ -25,7 +25,7 @@
 world-candidate = False
 
 # Again, not much to change here, though people might prefer a different name
-[everything]
+[all-installed]
 class = portage.sets.dbapi.EverythingSet
 world-candidate = False
 

Modified: main/branches/prefix/pym/_emerge/__init__.py
===================================================================
--- main/branches/prefix/pym/_emerge/__init__.py	2008-06-27 12:11:33 UTC (rev 10813)
+++ main/branches/prefix/pym/_emerge/__init__.py	2008-06-27 14:47:19 UTC (rev 10814)
@@ -1398,108 +1398,33 @@
 			return True
 		return False
 
-class _PackageMetadataWrapper(object):
+_all_metadata_keys = set(x for x in portage.auxdbkeys \
+	if not x.startswith("UNUSED_"))
+_all_metadata_keys.discard("CDEPEND")
+_all_metadata_keys.update(Package.metadata_keys)
+
+from portage.cache.mappings import slot_dict_class
+_PackageMetadataWrapperBase = slot_dict_class(_all_metadata_keys)
+
+class _PackageMetadataWrapper(_PackageMetadataWrapperBase):
 	"""
 	Detect metadata updates and synchronize Package attributes.
 	"""
-	_keys = set(x for x in portage.auxdbkeys \
-		if not x.startswith("UNUSED_"))
-	_keys.discard("CDEPEND")
-	_keys.update(Package.metadata_keys)
-	_keys = tuple(sorted(_keys))
-	__slots__ = ("__weakref__", "_pkg") + tuple("_val_" + k for k in _keys)
+
+	__slots__ = ("_pkg",)
 	_wrapped_keys = frozenset(
 		["COUNTER", "INHERITED", "IUSE", "SLOT", "USE", "_mtime_"])
 
 	def __init__(self, pkg, metadata):
+		_PackageMetadataWrapperBase.__init__(self)
 		self._pkg = pkg
 		self.update(metadata)
 
-	def __iter__(self):
-		for k, v in self.iteritems():
-			yield k
-
-	def __len__(self):
-		l = 0
-		for i in self.iteritems():
-			l += 1
-		return l
-
-	def keys(self):
-		return list(self)
-
-	def iteritems(self):
-		for k in self._keys:
-			try:
-				yield (k, getattr(self, "_val_" + k))
-			except AttributeError:
-				pass
-
-	def items(self):
-		return list(self.iteritems())
-
-	def itervalues(self):
-		for k, v in self.itervalues():
-			yield v
-
-	def values(self):
-		return list(self.itervalues())
-
-	def __delitem__(self, k):
-		try:
-			delattr(self, "_val_" + k)
-		except AttributeError:
-			raise KeyError(k)
-
 	def __setitem__(self, k, v):
-		setattr(self, "_val_" + k, v)
+		_PackageMetadataWrapperBase.__setitem__(self, k, v)
 		if k in self._wrapped_keys:
 			getattr(self, "_set_" + k.lower())(k, v)
 
-	def update(self, d):
-		i = getattr(d, "iteritems", None)
-		if i is None:
-			i = d
-		else:
-			i = i()
-		for k, v in i:
-			self[k] = v
-
-	def __getitem__(self, k):
-		try:
-			return getattr(self, "_val_" + k)
-		except AttributeError:
-			raise KeyError(k)
-
-	def get(self, key, default=None):
-		try:
-			return self[key]
-		except KeyError:
-			return default
-
-	def __contains__(self, k):
-		return hasattr(self, "_val_" + k)
-
-	def pop(self, key, *args):
-		if len(args) > 1:
-			raise TypeError("pop expected at most 2 arguments, got " + \
-				repr(1 + len(args)))
-		try:
-			value = self[key]
-		except KeyError:
-			if args:
-				return args[0]
-			raise
-		del self[key]
-		return value
-
-	def clear(self):
-		for k in self._keys:
-			try:
-				delattr(self, "_val_" + k)
-			except AttributError:
-				pass
-
 	def _set_inherited(self, k, v):
 		if isinstance(v, basestring):
 			v = frozenset(v.split())
@@ -3977,18 +3902,15 @@
 			if not isinstance(node, Package):
 				continue
 
-			# The visible packages cache has fullfilled it's purpose
-			# and it's no longer needed, so free the memory.
-			node.root_config.visible_pkgs.clear()
+			# The FakeVartree references the _package_cache which
+			# references the depgraph. So that Package instances don't
+			# hold the depgraph and FakeVartree on the heap, replace
+			# the RootConfig that references the FakeVartree with the
+			# original RootConfig instance which references the actual
+			# vartree.
+			node.root_config = \
+				self._trees_orig[node.root]["root_config"]
 
-			if isinstance(node.root_config.trees["vartree"], FakeVartree):
-				# The FakeVartree references the _package_cache which
-				# references the depgraph. So that Package instances don't
-				# hold the depgraph and FakeVartree on the heap, replace
-				# the FakeVartree reference with the real vartree.
-				node.root_config.trees["vartree"] = \
-					self._trees_orig[node.root]["vartree"]
-
 	def _resolve_conflicts(self):
 		if not self._complete_graph():
 			raise self._unknown_internal_error()

Modified: main/branches/prefix/pym/portage/__init__.py
===================================================================
--- main/branches/prefix/pym/portage/__init__.py	2008-06-27 12:11:33 UTC (rev 10813)
+++ main/branches/prefix/pym/portage/__init__.py	2008-06-27 14:47:19 UTC (rev 10814)
@@ -6993,6 +6993,54 @@
 			binarytree, myroot, mysettings["PKGDIR"], settings=mysettings)
 	return trees
 
+class _LegacyGlobalProxy(portage.util.ObjectProxy):
+	"""
+	Instances of these serve as proxies to global variables
+	that are initialized on demand.
+	"""
+	def __init__(self, name):
+		portage.util.ObjectProxy.__init__(self)
+		object.__setattr__(self, '_name', name)
+
+	def _get_target(self):
+		init_legacy_globals()
+		name = object.__getattribute__(self, '_name')
+		return globals()[name]
+
+class _PortdbProxy(portage.util.ObjectProxy):
+	"""
+	The portdb is initialized separately from the rest
+	of the variables, since sometimes the other variables
+	are needed while the portdb is not.
+	"""
+
+	def _get_target(self):
+		init_legacy_globals()
+		global db, portdb, root, _portdb_initialized
+		if not _portdb_initialized:
+			portdb = db[root]["porttree"].dbapi
+			_portdb_initialized = True
+		return portdb
+
+class _MtimedbProxy(portage.util.ObjectProxy):
+	"""
+	The mtimedb is independent from the portdb and other globals.
+	"""
+
+	def __init__(self, name):
+		portage.util.ObjectProxy.__init__(self)
+		object.__setattr__(self, '_name', name)
+
+	def _get_target(self):
+		global mtimedb, mtimedbfile, _mtimedb_initialized
+		if not _mtimedb_initialized:
+			mtimedbfile = os.path.join("/",
+				CACHE_PATH.lstrip(os.path.sep), "mtimedb")
+			mtimedb = MtimeDB(mtimedbfile)
+			_mtimedb_initialized = True
+		name = object.__getattribute__(self, '_name')
+		return globals()[name]
+
 # Initialization of legacy globals.  No functions/classes below this point
 # please!  When the above functions and classes become independent of the
 # below global variables, it will be possible to make the below code
@@ -7002,6 +7050,11 @@
 # overhead (and other issues!) of initializing the legacy globals.
 
 def init_legacy_globals():
+	global _globals_initialized
+	if _globals_initialized:
+		return
+	_globals_initialized = True
+
 	global db, settings, root, portdb, selinux_enabled, mtimedbfile, mtimedb, \
 	archlist, features, groups, pkglines, thirdpartymirrors, usedefaults, \
 	profiledir, flushmtimedb
@@ -7019,18 +7072,14 @@
 	del _initializing_globals
 
 	settings = db["/"]["vartree"].settings
-	portdb = db["/"]["porttree"].dbapi
 
 	for myroot in db:
 		if myroot != "/":
 			settings = db[myroot]["vartree"].settings
-			portdb = db[myroot]["porttree"].dbapi
 			break
 
 	root = settings["ROOT"]
 
-	mtimedbfile = os.path.join("/", CACHE_PATH.lstrip(os.path.sep), "mtimedb")
-	mtimedb = MtimeDB(mtimedbfile)
 
 	# ========================================================================
 	# COMPATIBILITY
@@ -7060,8 +7109,22 @@
 # use within Portage.  External use of this variable is unsupported because
 # it is experimental and it's behavior is likely to change.
 if "PORTAGE_LEGACY_GLOBALS" not in os.environ:
-	init_legacy_globals()
 
+	_mtimedb_initialized = False
+	mtimedb     = _MtimedbProxy("mtimedb")
+	mtimedbfile = _MtimedbProxy("mtimedbfile")
+
+	_portdb_initialized  = False
+	portdb = _PortdbProxy()
+
+	_globals_initialized = False
+
+	for k in ("db", "settings", "root", "selinux_enabled",
+		"archlist", "features", "groups",
+		"pkglines", "thirdpartymirrors", "usedefaults", "profiledir",
+		"flushmtimedb"):
+		globals()[k] = _LegacyGlobalProxy(k)
+
 # Clear the cache
 dircache={}
 

Modified: main/branches/prefix/pym/portage/cache/mappings.py
===================================================================
--- main/branches/prefix/pym/portage/cache/mappings.py	2008-06-27 12:11:33 UTC (rev 10813)
+++ main/branches/prefix/pym/portage/cache/mappings.py	2008-06-27 14:47:19 UTC (rev 10814)
@@ -4,6 +4,7 @@
 # $Id$
 
 import UserDict
+import weakref
 
 class ProtectedDict(UserDict.DictMixin):
 	"""
@@ -101,3 +102,140 @@
 			self.pull = None
 		return key in self.d
 
+_slot_dict_classes = weakref.WeakValueDictionary()
+
+def slot_dict_class(keys):
+	"""
+	Generates mapping classes that behave similar to a dict but store values
+	as object attributes that are allocated via __slots__. Instances of these
+	objects have a smaller memory footprint than a normal dict object.
+
+	@param keys: Fixed set of allowed keys
+	@type keys: iterable
+	@rtype: SlotDict
+	@returns: A class that constructs SlotDict instances
+		having the specified keys.
+	"""
+	if isinstance(keys, frozenset):
+		keys_set = keys
+	else:
+		keys_set = frozenset(keys)
+	v = _slot_dict_classes.get(keys_set)
+	if v is None:
+
+		class SlotDict(object):
+
+			allowed_keys = keys_set
+			__slots__ = ("__weakref__",) + \
+				tuple("_val_" + k for k in allowed_keys)
+
+			def __iter__(self):
+				for k, v in self.iteritems():
+					yield k
+
+			def __len__(self):
+				l = 0
+				for i in self.iteritems():
+					l += 1
+				return l
+
+			def keys(self):
+				return list(self)
+
+			def iteritems(self):
+				for k in self.allowed_keys:
+					try:
+						yield (k, getattr(self, "_val_" + k))
+					except AttributeError:
+						pass
+
+			def items(self):
+				return list(self.iteritems())
+
+			def itervalues(self):
+				for k, v in self.iteritems():
+					yield v
+
+			def values(self):
+				return list(self.itervalues())
+
+			def __delitem__(self, k):
+				try:
+					delattr(self, "_val_" + k)
+				except AttributeError:
+					raise KeyError(k)
+
+			def __setitem__(self, k, v):
+				setattr(self, "_val_" + k, v)
+
+			def setdefault(self, key, default=None):
+				try:
+					return self[key]
+				except KeyError:
+					self[key] = default
+				return default
+
+			def update(self, d):
+				i = getattr(d, "iteritems", None)
+				if i is None:
+					i = d
+				else:
+					i = i()
+				for k, v in i:
+					self[k] = v
+
+			def __getitem__(self, k):
+				try:
+					return getattr(self, "_val_" + k)
+				except AttributeError:
+					raise KeyError(k)
+
+			def get(self, key, default=None):
+				try:
+					return self[key]
+				except KeyError:
+					return default
+
+			def __contains__(self, k):
+				return hasattr(self, "_val_" + k)
+
+			def has_key(self, k):
+				return k in self
+
+			def pop(self, key, *args):
+				if len(args) > 1:
+					raise TypeError(
+						"pop expected at most 2 arguments, got " + \
+						repr(1 + len(args)))
+				try:
+					value = self[key]
+				except KeyError:
+					if args:
+						return args[0]
+					raise
+				del self[key]
+				return value
+
+			def popitem(self):
+				try:
+					k, v = self.iteritems().next()
+				except StopIteration:
+					raise KeyError('container is empty')
+				del self[k]
+				return (k, v)
+
+			def copy(self):
+				c = self.__class__()
+				c.update(self)
+				return c
+
+			def clear(self):
+				for k in self.allowed_keys:
+					try:
+						delattr(self, "_val_" + k)
+					except AttributeError:
+						pass
+
+		v = SlotDict
+		_slot_dict_classes[v.allowed_keys] = v
+	return v

Modified: main/branches/prefix/pym/portage/dbapi/bintree.py
===================================================================
--- main/branches/prefix/pym/portage/dbapi/bintree.py	2008-06-27 12:11:33 UTC (rev 10813)
+++ main/branches/prefix/pym/portage/dbapi/bintree.py	2008-06-27 14:47:19 UTC (rev 10814)
@@ -2,6 +2,7 @@
 # Distributed under the terms of the GNU General Public License v2
 # $Id$
 
+from portage.cache.mappings import slot_dict_class
 from portage.dep import isvalidatom, isjustname, dep_getkey, match_from_list
 from portage.dbapi.virtual import fakedbapi
 from portage.exception import InvalidPackageName, InvalidAtom, \
@@ -18,7 +19,7 @@
 
 import os, errno, stat
 import re
-from itertools import izip
+from itertools import chain, izip
 
 class bindbapi(fakedbapi):
 	_known_keys = frozenset(list(fakedbapi._known_keys) + \
@@ -35,6 +36,7 @@
 			"LICENSE", "PDEPEND", "PROVIDE",
 			"RDEPEND", "repository", "RESTRICT", "SLOT", "USE",
 			"EPREFIX"])
+		self._aux_cache_slot_dict = slot_dict_class(self._aux_cache_keys)
 		self._aux_cache = {}
 
 	def match(self, *pargs, **kwargs):
@@ -77,7 +79,7 @@
 			if not mydata.setdefault("EAPI", "0"):
 				mydata["EAPI"] = "0"
 		if cache_me:
-			aux_cache = {}
+			aux_cache = self._aux_cache_slot_dict()
 			for x in self._aux_cache_keys:
 				aux_cache[x] = mydata.get(x, "")
 			self._aux_cache[mycpv] = aux_cache
@@ -187,6 +189,16 @@
 				("repository"    ,   "REPO"),
 			)
 
+			self._pkgindex_allowed_pkg_keys = set(chain(
+				self._pkgindex_keys,
+				self._pkgindex_aux_keys,
+				self._pkgindex_hashes,
+				self._pkgindex_default_pkg_data,
+				self._pkgindex_inherited_keys,
+				self._pkgindex_default_header_data,
+				chain(*self._pkgindex_translated_keys)
+			))
+
 	def move_ent(self, mylist):
 		if not self.populated:
 			self.populate()
@@ -483,7 +495,7 @@
 									update_pkgindex = True
 							self.dbapi.cpv_inject(mycpv)
 							if not self.dbapi._aux_cache_keys.difference(d):
-								aux_cache = {}
+								aux_cache = self.dbapi._aux_cache_slot_dict()
 								for k in self.dbapi._aux_cache_keys:
 									aux_cache[k] = d[k]
 								self.dbapi._aux_cache[mycpv] = aux_cache
@@ -580,7 +592,7 @@
 						d.pop("PATH", None)
 					metadata[mycpv] = d
 					if not self.dbapi._aux_cache_keys.difference(d):
-						aux_cache = {}
+						aux_cache = self.dbapi._aux_cache_slot_dict()
 						for k in self.dbapi._aux_cache_keys:
 							aux_cache[k] = d[k]
 						self.dbapi._aux_cache[mycpv] = aux_cache
@@ -835,6 +847,7 @@
 
 	def _new_pkgindex(self):
 		return portage.getbinpkg.PackageIndex(
+			allowed_pkg_keys=self._pkgindex_allowed_pkg_keys,
 			default_header_data=self._pkgindex_default_header_data,
 			default_pkg_data=self._pkgindex_default_pkg_data,
 			inherited_keys=self._pkgindex_inherited_keys,

Modified: main/branches/prefix/pym/portage/dbapi/porttree.py
===================================================================
--- main/branches/prefix/pym/portage/dbapi/porttree.py	2008-06-27 12:11:33 UTC (rev 10813)
+++ main/branches/prefix/pym/portage/dbapi/porttree.py	2008-06-27 14:47:19 UTC (rev 10814)
@@ -3,6 +3,7 @@
 # $Id$
 
 from portage.cache.cache_errors import CacheError
+from portage.cache.mappings import slot_dict_class
 from portage.const import REPO_NAME_LOC
 from portage.data import portage_gid, secpass
 from portage.dbapi import dbapi
@@ -138,6 +139,10 @@
 			["DEPEND", "EAPI", "IUSE", "KEYWORDS", "LICENSE",
 			"PDEPEND", "PROVIDE", "RDEPEND", "repository",
 			"RESTRICT", "SLOT"])
+
+		# Repoman modifies _aux_cache_keys, so delay _aux_cache_slot_dict
+		# initialization until the first aux_get call.
+		self._aux_cache_slot_dict = None
 		self._aux_cache = {}
 		self._broken_ebuilds = set()
 
@@ -386,7 +391,10 @@
 				returnme.append(mydata.get(x,""))
 
 		if cache_me:
-			aux_cache = {}
+			if self._aux_cache_slot_dict is None:
+				self._aux_cache_slot_dict = \
+					slot_dict_class(self._aux_cache_keys)
+			aux_cache = self._aux_cache_slot_dict()
 			for x in self._aux_cache_keys:
 				aux_cache[x] = mydata.get(x, "")
 			self._aux_cache[mycpv] = aux_cache
@@ -866,4 +874,3 @@
 		except Exception, e:
 			pass
 		return myslot
-

Modified: main/branches/prefix/pym/portage/getbinpkg.py
===================================================================
--- main/branches/prefix/pym/portage/getbinpkg.py	2008-06-27 12:11:33 UTC (rev 10813)
+++ main/branches/prefix/pym/portage/getbinpkg.py	2008-06-27 14:47:19 UTC (rev 10814)
@@ -4,6 +4,7 @@
 # $Id$
 
 from portage.output import red, yellow, green
+from portage.cache.mappings import slot_dict_class
 import portage.xpak
 import HTMLParser
 import sys
@@ -681,8 +682,17 @@
 
 class PackageIndex(object):
 
-	def __init__(self, default_header_data=None, default_pkg_data=None,
-		inherited_keys=None, translated_keys=None):
+	def __init__(self,
+		allowed_pkg_keys=None,
+		default_header_data=None,
+		default_pkg_data=None,
+		inherited_keys=None,
+		translated_keys=None):
+
+		self._pkg_slot_dict = None
+		if allowed_pkg_keys is not None:
+			self._pkg_slot_dict = slot_dict_class(allowed_pkg_keys)
+
 		self._default_header_data = default_header_data
 		self._default_pkg_data = default_pkg_data
 		self._inherited_keys = inherited_keys
@@ -697,8 +707,15 @@
 		self.packages = []
 		self.modified = True
 
-	def _readpkgindex(self, pkgfile):
-		d = {}
+	def _readpkgindex(self, pkgfile, pkg_entry=True):
+
+		allowed_keys = None
+		if self._pkg_slot_dict is None or not pkg_entry:
+			d = {}
+		else:
+			d = self._pkg_slot_dict()
+			allowed_keys = d.allowed_keys
+
 		for line in pkgfile:
 			line = line.rstrip("\n")
 			if not line:
@@ -709,7 +726,11 @@
 			k, v = line
 			if v:
 				v = v[1:]
-			d[self._read_translation_map.get(k, k)] = v
+			k = self._read_translation_map.get(k, k)
+			if allowed_keys is not None and \
+				k not in allowed_keys:
+				continue
+			d[k] = v
 		return d
 
 	def _writepkgindex(self, pkgfile, items):
@@ -723,7 +744,7 @@
 		self.readBody(pkgfile)
 
 	def readHeader(self, pkgfile):
-		self.header.update(self._readpkgindex(pkgfile))
+		self.header.update(self._readpkgindex(pkgfile, pkg_entry=False))
 
 	def readBody(self, pkgfile):
 		while True:

Modified: main/branches/prefix/pym/portage/util.py
===================================================================
--- main/branches/prefix/pym/portage/util.py	2008-06-27 12:11:33 UTC (rev 10813)
+++ main/branches/prefix/pym/portage/util.py	2008-06-27 14:47:19 UTC (rev 10814)
@@ -913,6 +913,67 @@
 	perms_modified = apply_permissions(dir_path, *args, **kwargs)
 	return created_dir or perms_modified
 
+class ObjectProxy(object):
+
+	"""
+	Object that acts as a proxy to another object, forwarding
+	attribute accesses and method calls. This can be useful
+	for implementing lazy initialization.
+	"""
+
+	def _get_target(self):
+		raise NotImplementedError(self)
+
+	def __getattribute__(self, attr):
+		result = object.__getattribute__(self, '_get_target')()
+		return getattr(result, attr)
+
+	def __setattr__(self, attr, value):
+		result = object.__getattribute__(self, '_get_target')()
+		setattr(result, attr, value)
+
+	def __call__(self, *args, **kwargs):
+		result = object.__getattribute__(self, '_get_target')()
+		return result(*args, **kwargs)
+
+	def __setitem__(self, key, value):
+		object.__getattribute__(self, '_get_target')()[key] = value
+
+	def __getitem__(self, key):
+		return object.__getattribute__(self, '_get_target')()[key]
+
+	def __delitem__(self, key):
+		del object.__getattribute__(self, '_get_target')()[key]
+
+	def __contains__(self, key):
+		return key in object.__getattribute__(self, '_get_target')()
+
+	def __iter__(self):
+		return iter(object.__getattribute__(self, '_get_target')())
+
+	def __len__(self):
+		return len(object.__getattribute__(self, '_get_target')())
+
+	def __repr__(self):
+		return repr(object.__getattribute__(self, '_get_target')())
+
+	def __str__(self):
+		return str(object.__getattribute__(self, '_get_target')())
+
+	def __hash__(self):
+		return hash(object.__getattribute__(self, '_get_target')())
+
+	def __eq__(self, other):
+		return object.__getattribute__(self, '_get_target')() == other
+
+	def __ne__(self, other):
+		return object.__getattribute__(self, '_get_target')() != other
+
+	def __nonzero__(self):
+		if object.__getattribute__(self, '_get_target')():
+			return True
+		return False
+
 class LazyItemsDict(dict):
 	"""A mapping object that behaves like a standard dict except that it allows
 	for lazy initialization of values via callable objects.  Lazy items can be

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