# -*- coding: utf-8 -*-
"""The runtime functions and state used by compiled templates."""
import sys
from itertools import chain
from types import MethodType

from markupsafe import escape # noqa: F401
from markupsafe import Markup
from markupsafe import soft_unicode

from ._compat import abc
from ._compat import imap
from ._compat import implements_iterator
from ._compat import implements_to_string
from ._compat import iteritems
from ._compat import PY2
from ._compat import string_types
from ._compat import text_type
from ._compat import with_metaclass
from .exceptions import TemplateNotFound # noqa: F401
from .exceptions import TemplateRuntimeError # noqa: F401
from .exceptions import UndefinedError
from .nodes import EvalContext
from .utils import concat
from .utils import evalcontextfunction
from .utils import internalcode
from .utils import missing
from .utils import Namespace # noqa: F401
from .utils import object_type_repr

# these variables are exported to the template runtime
exported = [
 "LoopContext",
 "TemplateReference",
 "Macro",
 "Markup",
 "TemplateRuntimeError",
 "missing",
 "concat",
 "escape",
 "markup_join",
 "unicode_join",
 "to_string",
 "identity",
 "TemplateNotFound",
 "Namespace",
 "Undefined",
]

#: the name of the function that is used to convert something into
#: a string. We can just use the text type here.
to_string = text_type


def identity(x):
 """Returns its argument. Useful for certain things in the
 environment.
 """
 return x


def markup_join(seq):
 """Concatenation that escapes if necessary and converts to unicode."""
 buf = []
 iterator = imap(soft_unicode, seq)
 for arg in iterator:
 buf.append(arg)
 if hasattr(arg, "__html__"):
 return Markup(u"").join(chain(buf, iterator))
 return concat(buf)


def unicode_join(seq):
 """Simple args to unicode conversion and concatenation."""
 return concat(imap(text_type, seq))


def new_context(
 environment,
 template_name,
 blocks,
 vars=None,
 shared=None,
 globals=None,
 locals=None,
):
 """Internal helper for context creation."""
 if vars is None:
 vars = {}
 if shared:
 parent = vars
 else:
 parent = dict(globals or (), **vars)
 if locals:
 # if the parent is shared a copy should be created because
 # we don't want to modify the dict passed
 if shared:
 parent = dict(parent)
 for key, value in iteritems(locals):
 if value is not missing:
 parent[key] = value
 return environment.context_class(environment, parent, template_name, blocks)


class TemplateReference(object):
 """The `self` in templates."""

 def __init__(self, context):
 self.__context = context

 def __getitem__(self, name):
 blocks = self.__context.blocks[name]
 return BlockReference(name, self.__context, blocks, 0)

 def __repr__(self):
 return "<%s %r>" % (self.__class__.__name__, self.__context.name)


def _get_func(x):
 return getattr(x, "__func__", x)


class ContextMeta(type):
 def __new__(mcs, name, bases, d):
 rv = type.__new__(mcs, name, bases, d)
 if bases == ():
 return rv

 resolve = _get_func(rv.resolve)
 default_resolve = _get_func(Context.resolve)
 resolve_or_missing = _get_func(rv.resolve_or_missing)
 default_resolve_or_missing = _get_func(Context.resolve_or_missing)

 # If we have a changed resolve but no changed default or missing
 # resolve we invert the call logic.
 if (
 resolve is not default_resolve
 and resolve_or_missing is default_resolve_or_missing
 ):
 rv._legacy_resolve_mode = True
 elif (
 resolve is default_resolve
 and resolve_or_missing is default_resolve_or_missing
 ):
 rv._fast_resolve_mode = True

 return rv


def resolve_or_missing(context, key, missing=missing):
 if key in context.vars:
 return context.vars[key]
 if key in context.parent:
 return context.parent[key]
 return missing


class Context(with_metaclass(ContextMeta)):
 """The template context holds the variables of a template. It stores the
 values passed to the template and also the names the template exports.
 Creating instances is neither supported nor useful as it's created
 automatically at various stages of the template evaluation and should not
 be created by hand.

 The context is immutable. Modifications on :attr:`parent` **must not**
 happen and modifications on :attr:`vars` are allowed from generated
 template code only. Template filters and global functions marked as
 :func:`contextfunction`\\s get the active context passed as first argument
 and are allowed to access the context read-only.

 The template context supports read only dict operations (`get`,
 `keys`, `values`, `items`, `iterkeys`, `itervalues`, `iteritems`,
 `__getitem__`, `__contains__`). Additionally there is a :meth:`resolve`
 method that doesn't fail with a `KeyError` but returns an
 :class:`Undefined` object for missing variables.
 """

 # XXX: we want to eventually make this be a deprecation warning and
 # remove it.
 _legacy_resolve_mode = False
 _fast_resolve_mode = False

 def __init__(self, environment, parent, name, blocks):
 self.parent = parent
 self.vars = {}
 self.environment = environment
 self.eval_ctx = EvalContext(self.environment, name)
 self.exported_vars = set()
 self.name = name

 # create the initial mapping of blocks. Whenever template inheritance
 # takes place the runtime will update this mapping with the new blocks
 # from the template.
 self.blocks = dict((k, [v]) for k, v in iteritems(blocks))

 # In case we detect the fast resolve mode we can set up an alias
 # here that bypasses the legacy code logic.
 if self._fast_resolve_mode:
 self.resolve_or_missing = MethodType(resolve_or_missing, self)

 def super(self, name, current):
 """Render a parent block."""
 try:
 blocks = self.blocks[name]
 index = blocks.index(current) + 1
 blocks[index]
 except LookupError:
 return self.environment.undefined(
 "there is no parent block called %r." % name, name="super"
 )
 return BlockReference(name, self, blocks, index)

 def get(self, key, default=None):
 """Returns an item from the template context, if it doesn't exist
 `default` is returned.
 """
 try:
 return self[key]
 except KeyError:
 return default

 def resolve(self, key):
 """Looks up a variable like `__getitem__` or `get` but returns an
 :class:`Undefined` object with the name of the name looked up.
 """
 if self._legacy_resolve_mode:
 rv = resolve_or_missing(self, key)
 else:
 rv = self.resolve_or_missing(key)
 if rv is missing:
 return self.environment.undefined(name=key)
 return rv

 def resolve_or_missing(self, key):
 """Resolves a variable like :meth:`resolve` but returns the
 special `missing` value if it cannot be found.
 """
 if self._legacy_resolve_mode:
 rv = self.resolve(key)
 if isinstance(rv, Undefined):
 rv = missing
 return rv
 return resolve_or_missing(self, key)

 def get_exported(self):
 """Get a new dict with the exported variables."""
 return dict((k, self.vars[k]) for k in self.exported_vars)

 def get_all(self):
 """Return the complete context as dict including the exported
 variables. For optimizations reasons this might not return an
 actual copy so be careful with using it.
 """
 if not self.vars:
 return self.parent
 if not self.parent:
 return self.vars
 return dict(self.parent, **self.vars)

 @internalcode
 def call(__self, __obj, *args, **kwargs): # noqa: B902
 """Call the callable with the arguments and keyword arguments
 provided but inject the active context or environment as first
 argument if the callable is a :func:`contextfunction` or
 :func:`environmentfunction`.
 """
 if __debug__:
 __traceback_hide__ = True # noqa

 # Allow callable classes to take a context
 if hasattr(__obj, "__call__"): # noqa: B004
 fn = __obj.__call__
 for fn_type in (
 "contextfunction",
 "evalcontextfunction",
 "environmentfunction",
 ):
 if hasattr(fn, fn_type):
 __obj = fn
 break

 if callable(__obj):
 if getattr(__obj, "contextfunction", False) is True:
 args = (__self,) + args
 elif getattr(__obj, "evalcontextfunction", False) is True:
 args = (__self.eval_ctx,) + args
 elif getattr(__obj, "environmentfunction", False) is True:
 args = (__self.environment,) + args
 try:
 return __obj(*args, **kwargs)
 except StopIteration:
 return __self.environment.undefined(
 "value was undefined because "
 "a callable raised a "
 "StopIteration exception"
 )

 def derived(self, locals=None):
 """Internal helper function to create a derived context. This is
 used in situations where the system needs a new context in the same
 template that is independent.
 """
 context = new_context(
 self.environment, self.name, {}, self.get_all(), True, None, locals
 )
 context.eval_ctx = self.eval_ctx
 context.blocks.update((k, list(v)) for k, v in iteritems(self.blocks))
 return context

 def _all(meth): # noqa: B902
 def proxy(self):
 return getattr(self.get_all(), meth)()

 proxy.__doc__ = getattr(dict, meth).__doc__
 proxy.__name__ = meth
 return proxy

 keys = _all("keys")
 values = _all("values")
 items = _all("items")

 # not available on python 3
 if PY2:
 iterkeys = _all("iterkeys")
 itervalues = _all("itervalues")
 iteritems = _all("iteritems")
 del _all

 def __contains__(self, name):
 return name in self.vars or name in self.parent

 def __getitem__(self, key):
 """Lookup a variable or raise `KeyError` if the variable is
 undefined.
 """
 item = self.resolve_or_missing(key)
 if item is missing:
 raise KeyError(key)
 return item

 def __repr__(self):
 return "<%s %s of %r>" % (
 self.__class__.__name__,
 repr(self.get_all()),
 self.name,
 )


abc.Mapping.register(Context)


class BlockReference(object):
 """One block on a template reference."""

 def __init__(self, name, context, stack, depth):
 self.name = name
 self._context = context
 self._stack = stack
 self._depth = depth

 @property
 def super(self):
 """Super the block."""
 if self._depth + 1 >= len(self._stack):
 return self._context.environment.undefined(
 "there is no parent block called %r." % self.name, name="super"
 )
 return BlockReference(self.name, self._context, self._stack, self._depth + 1)

 @internalcode
 def __call__(self):
 rv = concat(self._stack[self._depth](self._context))
 if self._context.eval_ctx.autoescape:
 rv = Markup(rv)
 return rv


@implements_iterator
class LoopContext:
 """A wrapper iterable for dynamic ``for`` loops, with information
 about the loop and iteration.
 """

 #: Current iteration of the loop, starting at 0.
 index0 = -1

 _length = None
 _after = missing
 _current = missing
 _before = missing
 _last_changed_value = missing

 def __init__(self, iterable, undefined, recurse=None, depth0=0):
 """
 :param iterable: Iterable to wrap.
 :param undefined: :class:`Undefined` class to use for next and
 previous items.
 :param recurse: The function to render the loop body when the
 loop is marked recursive.
 :param depth0: Incremented when looping recursively.
 """
 self._iterable = iterable
 self._iterator = self._to_iterator(iterable)
 self._undefined = undefined
 self._recurse = recurse
 #: How many levels deep a recursive loop currently is, starting at 0.
 self.depth0 = depth0

 @staticmethod
 def _to_iterator(iterable):
 return iter(iterable)

 @property
 def length(self):
 """Length of the iterable.

 If the iterable is a generator or otherwise does not have a
 size, it is eagerly evaluated to get a size.
 """
 if self._length is not None:
 return self._length

 try:
 self._length = len(self._iterable)
 except TypeError:
 iterable = list(self._iterator)
 self._iterator = self._to_iterator(iterable)
 self._length = len(iterable) + self.index + (self._after is not missing)

 return self._length

 def __len__(self):
 return self.length

 @property
 def depth(self):
 """How many levels deep a recursive loop currently is, starting at 1."""
 return self.depth0 + 1

 @property
 def index(self):
 """Current iteration of the loop, starting at 1."""
 return self.index0 + 1

 @property
 def revindex0(self):
 """Number of iterations from the end of the loop, ending at 0.

 Requires calculating :attr:`length`.
 """
 return self.length - self.index

 @property
 def revindex(self):
 """Number of iterations from the end of the loop, ending at 1.

 Requires calculating :attr:`length`.
 """
 return self.length - self.index0

 @property
 def first(self):
 """Whether this is the first iteration of the loop."""
 return self.index0 == 0

 def _peek_next(self):
 """Return the next element in the iterable, or :data:`missing`
 if the iterable is exhausted. Only peeks one item ahead, caching
 the result in :attr:`_last` for use in subsequent checks. The
 cache is reset when :meth:`__next__` is called.
 """
 if self._after is not missing:
 return self._after

 self._after = next(self._iterator, missing)
 return self._after

 @property
 def last(self):
 """Whether this is the last iteration of the loop.

 Causes the iterable to advance early. See
 :func:`itertools.groupby` for issues this can cause.
 The :func:`groupby` filter avoids that issue.
 """
 return self._peek_next() is missing

 @property
 def previtem(self):
 """The item in the previous iteration. Undefined during the
 first iteration.
 """
 if self.first:
 return self._undefined("there is no previous item")

 return self._before

 @property
 def nextitem(self):
 """The item in the next iteration. Undefined during the last
 iteration.

 Causes the iterable to advance early. See
 :func:`itertools.groupby` for issues this can cause.
 The :func:`groupby` filter avoids that issue.
 """
 rv = self._peek_next()

 if rv is missing:
 return self._undefined("there is no next item")

 return rv

 def cycle(self, *args):
 """Return a value from the given args, cycling through based on
 the current :attr:`index0`.

 :param args: One or more values to cycle through.
 """
 if not args:
 raise TypeError("no items for cycling given")

 return args[self.index0 % len(args)]

 def changed(self, *value):
 """Return ``True`` if previously called with a different value
 (including when called for the first time).

 :param value: One or more values to compare to the last call.
 """
 if self._last_changed_value != value:
 self._last_changed_value = value
 return True

 return False

 def __iter__(self):
 return self

 def __next__(self):
 if self._after is not missing:
 rv = self._after
 self._after = missing
 else:
 rv = next(self._iterator)

 self.index0 += 1
 self._before = self._current
 self._current = rv
 return rv, self

 @internalcode
 def __call__(self, iterable):
 """When iterating over nested data, render the body of the loop
 recursively with the given inner iterable data.

 The loop must have the ``recursive`` marker for this to work.
 """
 if self._recurse is None:
 raise TypeError(
 "The loop must have the 'recursive' marker to be called recursively."
 )

 return self._recurse(iterable, self._recurse, depth=self.depth)

 def __repr__(self):
 return "<%s %d/%d>" % (self.__class__.__name__, self.index, self.length)


class Macro(object):
 """Wraps a macro function."""

 def __init__(
 self,
 environment,
 func,
 name,
 arguments,
 catch_kwargs,
 catch_varargs,
 caller,
 default_autoescape=None,
 ):
 self._environment = environment
 self._func = func
 self._argument_count = len(arguments)
 self.name = name
 self.arguments = arguments
 self.catch_kwargs = catch_kwargs
 self.catch_varargs = catch_varargs
 self.caller = caller
 self.explicit_caller = "caller" in arguments
 if default_autoescape is None:
 default_autoescape = environment.autoescape
 self._default_autoescape = default_autoescape

 @internalcode
 @evalcontextfunction
 def __call__(self, *args, **kwargs):
 # This requires a bit of explanation, In the past we used to
 # decide largely based on compile-time information if a macro is
 # safe or unsafe. While there was a volatile mode it was largely
 # unused for deciding on escaping. This turns out to be
 # problematic for macros because whether a macro is safe depends not
 # on the escape mode when it was defined, but rather when it was used.
 #
 # Because however we export macros from the module system and
 # there are historic callers that do not pass an eval context (and
 # will continue to not pass one), we need to perform an instance
 # check here.
 #
 # This is considered safe because an eval context is not a valid
 # argument to callables otherwise anyway. Worst case here is
 # that if no eval context is passed we fall back to the compile
 # time autoescape flag.
 if args and isinstance(args[0], EvalContext):
 autoescape = args[0].autoescape
 args = args[1:]
 else:
 autoescape = self._default_autoescape

 # try to consume the positional arguments
 arguments = list(args[: self._argument_count])
 off = len(arguments)

 # For information why this is necessary refer to the handling
 # of caller in the `macro_body` handler in the compiler.
 found_caller = False

 # if the number of arguments consumed is not the number of
 # arguments expected we start filling in keyword arguments
 # and defaults.
 if off != self._argument_count:
 for name in self.arguments[len(arguments) :]:
 try:
 value = kwargs.pop(name)
 except KeyError:
 value = missing
 if name == "caller":
 found_caller = True
 arguments.append(value)
 else:
 found_caller = self.explicit_caller

 # it's important that the order of these arguments does not change
 # if not also changed in the compiler's `function_scoping` method.
 # the order is caller, keyword arguments, positional arguments!
 if self.caller and not found_caller:
 caller = kwargs.pop("caller", None)
 if caller is None:
 caller = self._environment.undefined("No caller defined", name="caller")
 arguments.append(caller)

 if self.catch_kwargs:
 arguments.append(kwargs)
 elif kwargs:
 if "caller" in kwargs:
 raise TypeError(
 "macro %r was invoked with two values for "
 "the special caller argument. This is "
 "most likely a bug." % self.name
 )
 raise TypeError(
 "macro %r takes no keyword argument %r"
 % (self.name, next(iter(kwargs)))
 )
 if self.catch_varargs:
 arguments.append(args[self._argument_count :])
 elif len(args) > self._argument_count:
 raise TypeError(
 "macro %r takes not more than %d argument(s)"
 % (self.name, len(self.arguments))
 )

 return self._invoke(arguments, autoescape)

 def _invoke(self, arguments, autoescape):
 """This method is being swapped out by the async implementation."""
 rv = self._func(*arguments)
 if autoescape:
 rv = Markup(rv)
 return rv

 def __repr__(self):
 return "<%s %s>" % (
 self.__class__.__name__,
 self.name is None and "anonymous" or repr(self.name),
 )


@implements_to_string
class Undefined(object):
 """The default undefined type. This undefined type can be printed and
 iterated over, but every other access will raise an :exc:`UndefinedError`:

 >>> foo = Undefined(name='foo')
 >>> str(foo)
 ''
 >>> not foo
 True
 >>> foo + 42
 Traceback (most recent call last):
 ...
 jinja2.exceptions.UndefinedError: 'foo' is undefined
 """

 __slots__ = (
 "_undefined_hint",
 "_undefined_obj",
 "_undefined_name",
 "_undefined_exception",
 )

 def __init__(self, hint=None, obj=missing, name=None, exc=UndefinedError):
 self._undefined_hint = hint
 self._undefined_obj = obj
 self._undefined_name = name
 self._undefined_exception = exc

 @property
 def _undefined_message(self):
 """Build a message about the undefined value based on how it was
 accessed.
 """
 if self._undefined_hint:
 return self._undefined_hint

 if self._undefined_obj is missing:
 return "%r is undefined" % self._undefined_name

 if not isinstance(self._undefined_name, string_types):
 return "%s has no element %r" % (
 object_type_repr(self._undefined_obj),
 self._undefined_name,
 )

 return "%r has no attribute %r" % (
 object_type_repr(self._undefined_obj),
 self._undefined_name,
 )

 @internalcode
 def _fail_with_undefined_error(self, *args, **kwargs):
 """Raise an :exc:`UndefinedError` when operations are performed
 on the undefined value.
 """
 raise self._undefined_exception(self._undefined_message)

 @internalcode
 def __getattr__(self, name):
 if name[:2] == "__":
 raise AttributeError(name)
 return self._fail_with_undefined_error()

 __add__ = (
 __radd__
 ) = (
 __mul__
 ) = (
 __rmul__
 ) = (
 __div__
 ) = (
 __rdiv__
 ) = (
 __truediv__
 ) = (
 __rtruediv__
 ) = (
 __floordiv__
 ) = (
 __rfloordiv__
 ) = (
 __mod__
 ) = (
 __rmod__
 ) = (
 __pos__
 ) = (
 __neg__
 ) = (
 __call__
 ) = (
 __getitem__
 ) = (
 __lt__
 ) = (
 __le__
 ) = (
 __gt__
 ) = (
 __ge__
 ) = (
 __int__
 ) = (
 __float__
 ) = (
 __complex__
 ) = __pow__ = __rpow__ = __sub__ = __rsub__ = _fail_with_undefined_error

 def __eq__(self, other):
 return type(self) is type(other)

 def __ne__(self, other):
 return not self.__eq__(other)

 def __hash__(self):
 return id(type(self))

 def __str__(self):
 return u""

 def __len__(self):
 return 0

 def __iter__(self):
 if 0:
 yield None

 def __nonzero__(self):
 return False

 __bool__ = __nonzero__

 def __repr__(self):
 return "Undefined"


def make_logging_undefined(logger=None, base=None):
 """Given a logger object this returns a new undefined class that will
 log certain failures. It will log iterations and printing. If no
 logger is given a default logger is created.

 Example::

 logger = logging.getLogger(__name__)
 LoggingUndefined = make_logging_undefined(
 logger=logger,
 base=Undefined
 )

 .. versionadded:: 2.8

 :param logger: the logger to use. If not provided, a default logger
 is created.
 :param base: the base class to add logging functionality to. This
 defaults to :class:`Undefined`.
 """
 if logger is None:
 import logging

 logger = logging.getLogger(__name__)
 logger.addHandler(logging.StreamHandler(sys.stderr))
 if base is None:
 base = Undefined

 def _log_message(undef):
 if undef._undefined_hint is None:
 if undef._undefined_obj is missing:
 hint = "%s is undefined" % undef._undefined_name
 elif not isinstance(undef._undefined_name, string_types):
 hint = "%s has no element %s" % (
 object_type_repr(undef._undefined_obj),
 undef._undefined_name,
 )
 else:
 hint = "%s has no attribute %s" % (
 object_type_repr(undef._undefined_obj),
 undef._undefined_name,
 )
 else:
 hint = undef._undefined_hint
 logger.warning("Template variable warning: %s", hint)

 class LoggingUndefined(base):
 def _fail_with_undefined_error(self, *args, **kwargs):
 try:
 return base._fail_with_undefined_error(self, *args, **kwargs)
 except self._undefined_exception as e:
 logger.error("Template variable error: %s", str(e))
 raise e

 def __str__(self):
 rv = base.__str__(self)
 _log_message(self)
 return rv

 def __iter__(self):
 rv = base.__iter__(self)
 _log_message(self)
 return rv

 if PY2:

 def __nonzero__(self):
 rv = base.__nonzero__(self)
 _log_message(self)
 return rv

 def __unicode__(self):
 rv = base.__unicode__(self)
 _log_message(self)
 return rv

 else:

 def __bool__(self):
 rv = base.__bool__(self)
 _log_message(self)
 return rv

 return LoggingUndefined


# No @implements_to_string decorator here because __str__
# is not overwritten from Undefined in this class.
# This would cause a recursion error in Python 2.
class ChainableUndefined(Undefined):
 """An undefined that is chainable, where both ``__getattr__`` and
 ``__getitem__`` return itself rather than raising an
 :exc:`UndefinedError`.

 >>> foo = ChainableUndefined(name='foo')
 >>> str(foo.bar['baz'])
 ''
 >>> foo.bar['baz'] + 42
 Traceback (most recent call last):
 ...
 jinja2.exceptions.UndefinedError: 'foo' is undefined

 .. versionadded:: 2.11.0
 """

 __slots__ = ()

 def __html__(self):
 return self.__str__()

 def __getattr__(self, _):
 return self

 __getitem__ = __getattr__


@implements_to_string
class DebugUndefined(Undefined):
 """An undefined that returns the debug info when printed.

 >>> foo = DebugUndefined(name='foo')
 >>> str(foo)
 '{{ foo }}'
 >>> not foo
 True
 >>> foo + 42
 Traceback (most recent call last):
 ...
 jinja2.exceptions.UndefinedError: 'foo' is undefined
 """

 __slots__ = ()

 def __str__(self):
 if self._undefined_hint is None:
 if self._undefined_obj is missing:
 return u"{{ %s }}" % self._undefined_name
 return "{{ no such element: %s[%r] }}" % (
 object_type_repr(self._undefined_obj),
 self._undefined_name,
 )
 return u"{{ undefined value printed: %s }}" % self._undefined_hint


@implements_to_string
class StrictUndefined(Undefined):
 """An undefined that barks on print and iteration as well as boolean
 tests and all kinds of comparisons. In other words: you can do nothing
 with it except checking if it's defined using the `defined` test.

 >>> foo = StrictUndefined(name='foo')
 >>> str(foo)
 Traceback (most recent call last):
 ...
 jinja2.exceptions.UndefinedError: 'foo' is undefined
 >>> not foo
 Traceback (most recent call last):
 ...
 jinja2.exceptions.UndefinedError: 'foo' is undefined
 >>> foo + 42
 Traceback (most recent call last):
 ...
 jinja2.exceptions.UndefinedError: 'foo' is undefined
 """

 __slots__ = ()
 __iter__ = (
 __str__
 ) = (
 __len__
 ) = (
 __nonzero__
 ) = __eq__ = __ne__ = __bool__ = __hash__ = Undefined._fail_with_undefined_error


# remove remaining slots attributes, after the metaclass did the magic they
# are unneeded and irritating as they contain wrong data for the subclasses.
del (
 Undefined.__slots__,
 ChainableUndefined.__slots__,
 DebugUndefined.__slots__,
 StrictUndefined.__slots__,
)