--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.7/site-packages/jinja2/runtime.py	Sat May 02 07:14:21 2020 -0400
@@ -0,0 +1,1011 @@
+# -*- 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__,
+)