diff venv/lib/python2.7/site-packages/jinja2/nodes.py @ 0:d67268158946 draft

planemo upload commit a3f181f5f126803c654b3a66dd4e83a48f7e203b

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/venv/lib/python2.7/site-packages/jinja2/nodes.py	Mon Oct 12 17:43:33 2015 -0400
@@ -0,0 +1,919 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.nodes
+    ~~~~~~~~~~~~
+
+    This module implements additional nodes derived from the ast base node.
+
+    It also provides some node tree helper functions like `in_lineno` and
+    `get_nodes` used by the parser and translator in order to normalize
+    python and jinja nodes.
+
+    :copyright: (c) 2010 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import types
+import operator
+
+from collections import deque
+from jinja2.utils import Markup
+from jinja2._compat import izip, with_metaclass, text_type
+
+
+#: the types we support for context functions
+_context_function_types = (types.FunctionType, types.MethodType)
+
+
+_binop_to_func = {
+    '*':        operator.mul,
+    '/':        operator.truediv,
+    '//':       operator.floordiv,
+    '**':       operator.pow,
+    '%':        operator.mod,
+    '+':        operator.add,
+    '-':        operator.sub
+}
+
+_uaop_to_func = {
+    'not':      operator.not_,
+    '+':        operator.pos,
+    '-':        operator.neg
+}
+
+_cmpop_to_func = {
+    'eq':       operator.eq,
+    'ne':       operator.ne,
+    'gt':       operator.gt,
+    'gteq':     operator.ge,
+    'lt':       operator.lt,
+    'lteq':     operator.le,
+    'in':       lambda a, b: a in b,
+    'notin':    lambda a, b: a not in b
+}
+
+
+class Impossible(Exception):
+    """Raised if the node could not perform a requested action."""
+
+
+class NodeType(type):
+    """A metaclass for nodes that handles the field and attribute
+    inheritance.  fields and attributes from the parent class are
+    automatically forwarded to the child."""
+
+    def __new__(cls, name, bases, d):
+        for attr in 'fields', 'attributes':
+            storage = []
+            storage.extend(getattr(bases[0], attr, ()))
+            storage.extend(d.get(attr, ()))
+            assert len(bases) == 1, 'multiple inheritance not allowed'
+            assert len(storage) == len(set(storage)), 'layout conflict'
+            d[attr] = tuple(storage)
+        d.setdefault('abstract', False)
+        return type.__new__(cls, name, bases, d)
+
+
+class EvalContext(object):
+    """Holds evaluation time information.  Custom attributes can be attached
+    to it in extensions.
+    """
+
+    def __init__(self, environment, template_name=None):
+        self.environment = environment
+        if callable(environment.autoescape):
+            self.autoescape = environment.autoescape(template_name)
+        else:
+            self.autoescape = environment.autoescape
+        self.volatile = False
+
+    def save(self):
+        return self.__dict__.copy()
+
+    def revert(self, old):
+        self.__dict__.clear()
+        self.__dict__.update(old)
+
+
+def get_eval_context(node, ctx):
+    if ctx is None:
+        if node.environment is None:
+            raise RuntimeError('if no eval context is passed, the '
+                               'node must have an attached '
+                               'environment.')
+        return EvalContext(node.environment)
+    return ctx
+
+
+class Node(with_metaclass(NodeType, object)):
+    """Baseclass for all Jinja2 nodes.  There are a number of nodes available
+    of different types.  There are four major types:
+
+    -   :class:`Stmt`: statements
+    -   :class:`Expr`: expressions
+    -   :class:`Helper`: helper nodes
+    -   :class:`Template`: the outermost wrapper node
+
+    All nodes have fields and attributes.  Fields may be other nodes, lists,
+    or arbitrary values.  Fields are passed to the constructor as regular
+    positional arguments, attributes as keyword arguments.  Each node has
+    two attributes: `lineno` (the line number of the node) and `environment`.
+    The `environment` attribute is set at the end of the parsing process for
+    all nodes automatically.
+    """
+    fields = ()
+    attributes = ('lineno', 'environment')
+    abstract = True
+
+    def __init__(self, *fields, **attributes):
+        if self.abstract:
+            raise TypeError('abstract nodes are not instanciable')
+        if fields:
+            if len(fields) != len(self.fields):
+                if not self.fields:
+                    raise TypeError('%r takes 0 arguments' %
+                                    self.__class__.__name__)
+                raise TypeError('%r takes 0 or %d argument%s' % (
+                    self.__class__.__name__,
+                    len(self.fields),
+                    len(self.fields) != 1 and 's' or ''
+                ))
+            for name, arg in izip(self.fields, fields):
+                setattr(self, name, arg)
+        for attr in self.attributes:
+            setattr(self, attr, attributes.pop(attr, None))
+        if attributes:
+            raise TypeError('unknown attribute %r' %
+                            next(iter(attributes)))
+
+    def iter_fields(self, exclude=None, only=None):
+        """This method iterates over all fields that are defined and yields
+        ``(key, value)`` tuples.  Per default all fields are returned, but
+        it's possible to limit that to some fields by providing the `only`
+        parameter or to exclude some using the `exclude` parameter.  Both
+        should be sets or tuples of field names.
+        """
+        for name in self.fields:
+            if (exclude is only is None) or \
+               (exclude is not None and name not in exclude) or \
+               (only is not None and name in only):
+                try:
+                    yield name, getattr(self, name)
+                except AttributeError:
+                    pass
+
+    def iter_child_nodes(self, exclude=None, only=None):
+        """Iterates over all direct child nodes of the node.  This iterates
+        over all fields and yields the values of they are nodes.  If the value
+        of a field is a list all the nodes in that list are returned.
+        """
+        for field, item in self.iter_fields(exclude, only):
+            if isinstance(item, list):
+                for n in item:
+                    if isinstance(n, Node):
+                        yield n
+            elif isinstance(item, Node):
+                yield item
+
+    def find(self, node_type):
+        """Find the first node of a given type.  If no such node exists the
+        return value is `None`.
+        """
+        for result in self.find_all(node_type):
+            return result
+
+    def find_all(self, node_type):
+        """Find all the nodes of a given type.  If the type is a tuple,
+        the check is performed for any of the tuple items.
+        """
+        for child in self.iter_child_nodes():
+            if isinstance(child, node_type):
+                yield child
+            for result in child.find_all(node_type):
+                yield result
+
+    def set_ctx(self, ctx):
+        """Reset the context of a node and all child nodes.  Per default the
+        parser will all generate nodes that have a 'load' context as it's the
+        most common one.  This method is used in the parser to set assignment
+        targets and other nodes to a store context.
+        """
+        todo = deque([self])
+        while todo:
+            node = todo.popleft()
+            if 'ctx' in node.fields:
+                node.ctx = ctx
+            todo.extend(node.iter_child_nodes())
+        return self
+
+    def set_lineno(self, lineno, override=False):
+        """Set the line numbers of the node and children."""
+        todo = deque([self])
+        while todo:
+            node = todo.popleft()
+            if 'lineno' in node.attributes:
+                if node.lineno is None or override:
+                    node.lineno = lineno
+            todo.extend(node.iter_child_nodes())
+        return self
+
+    def set_environment(self, environment):
+        """Set the environment for all nodes."""
+        todo = deque([self])
+        while todo:
+            node = todo.popleft()
+            node.environment = environment
+            todo.extend(node.iter_child_nodes())
+        return self
+
+    def __eq__(self, other):
+        return type(self) is type(other) and \
+               tuple(self.iter_fields()) == tuple(other.iter_fields())
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    # Restore Python 2 hashing behavior on Python 3
+    __hash__ = object.__hash__
+
+    def __repr__(self):
+        return '%s(%s)' % (
+            self.__class__.__name__,
+            ', '.join('%s=%r' % (arg, getattr(self, arg, None)) for
+                      arg in self.fields)
+        )
+
+
+class Stmt(Node):
+    """Base node for all statements."""
+    abstract = True
+
+
+class Helper(Node):
+    """Nodes that exist in a specific context only."""
+    abstract = True
+
+
+class Template(Node):
+    """Node that represents a template.  This must be the outermost node that
+    is passed to the compiler.
+    """
+    fields = ('body',)
+
+
+class Output(Stmt):
+    """A node that holds multiple expressions which are then printed out.
+    This is used both for the `print` statement and the regular template data.
+    """
+    fields = ('nodes',)
+
+
+class Extends(Stmt):
+    """Represents an extends statement."""
+    fields = ('template',)
+
+
+class For(Stmt):
+    """The for loop.  `target` is the target for the iteration (usually a
+    :class:`Name` or :class:`Tuple`), `iter` the iterable.  `body` is a list
+    of nodes that are used as loop-body, and `else_` a list of nodes for the
+    `else` block.  If no else node exists it has to be an empty list.
+
+    For filtered nodes an expression can be stored as `test`, otherwise `None`.
+    """
+    fields = ('target', 'iter', 'body', 'else_', 'test', 'recursive')
+
+
+class If(Stmt):
+    """If `test` is true, `body` is rendered, else `else_`."""
+    fields = ('test', 'body', 'else_')
+
+
+class Macro(Stmt):
+    """A macro definition.  `name` is the name of the macro, `args` a list of
+    arguments and `defaults` a list of defaults if there are any.  `body` is
+    a list of nodes for the macro body.
+    """
+    fields = ('name', 'args', 'defaults', 'body')
+
+
+class CallBlock(Stmt):
+    """Like a macro without a name but a call instead.  `call` is called with
+    the unnamed macro as `caller` argument this node holds.
+    """
+    fields = ('call', 'args', 'defaults', 'body')
+
+
+class FilterBlock(Stmt):
+    """Node for filter sections."""
+    fields = ('body', 'filter')
+
+
+class Block(Stmt):
+    """A node that represents a block."""
+    fields = ('name', 'body', 'scoped')
+
+
+class Include(Stmt):
+    """A node that represents the include tag."""
+    fields = ('template', 'with_context', 'ignore_missing')
+
+
+class Import(Stmt):
+    """A node that represents the import tag."""
+    fields = ('template', 'target', 'with_context')
+
+
+class FromImport(Stmt):
+    """A node that represents the from import tag.  It's important to not
+    pass unsafe names to the name attribute.  The compiler translates the
+    attribute lookups directly into getattr calls and does *not* use the
+    subscript callback of the interface.  As exported variables may not
+    start with double underscores (which the parser asserts) this is not a
+    problem for regular Jinja code, but if this node is used in an extension
+    extra care must be taken.
+
+    The list of names may contain tuples if aliases are wanted.
+    """
+    fields = ('template', 'names', 'with_context')
+
+
+class ExprStmt(Stmt):
+    """A statement that evaluates an expression and discards the result."""
+    fields = ('node',)
+
+
+class Assign(Stmt):
+    """Assigns an expression to a target."""
+    fields = ('target', 'node')
+
+
+class AssignBlock(Stmt):
+    """Assigns a block to a target."""
+    fields = ('target', 'body')
+
+
+class Expr(Node):
+    """Baseclass for all expressions."""
+    abstract = True
+
+    def as_const(self, eval_ctx=None):
+        """Return the value of the expression as constant or raise
+        :exc:`Impossible` if this was not possible.
+
+        An :class:`EvalContext` can be provided, if none is given
+        a default context is created which requires the nodes to have
+        an attached environment.
+
+        .. versionchanged:: 2.4
+           the `eval_ctx` parameter was added.
+        """
+        raise Impossible()
+
+    def can_assign(self):
+        """Check if it's possible to assign something to this node."""
+        return False
+
+
+class BinExpr(Expr):
+    """Baseclass for all binary expressions."""
+    fields = ('left', 'right')
+    operator = None
+    abstract = True
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        # intercepted operators cannot be folded at compile time
+        if self.environment.sandboxed and \
+           self.operator in self.environment.intercepted_binops:
+            raise Impossible()
+        f = _binop_to_func[self.operator]
+        try:
+            return f(self.left.as_const(eval_ctx), self.right.as_const(eval_ctx))
+        except Exception:
+            raise Impossible()
+
+
+class UnaryExpr(Expr):
+    """Baseclass for all unary expressions."""
+    fields = ('node',)
+    operator = None
+    abstract = True
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        # intercepted operators cannot be folded at compile time
+        if self.environment.sandboxed and \
+           self.operator in self.environment.intercepted_unops:
+            raise Impossible()
+        f = _uaop_to_func[self.operator]
+        try:
+            return f(self.node.as_const(eval_ctx))
+        except Exception:
+            raise Impossible()
+
+
+class Name(Expr):
+    """Looks up a name or stores a value in a name.
+    The `ctx` of the node can be one of the following values:
+
+    -   `store`: store a value in the name
+    -   `load`: load that name
+    -   `param`: like `store` but if the name was defined as function parameter.
+    """
+    fields = ('name', 'ctx')
+
+    def can_assign(self):
+        return self.name not in ('true', 'false', 'none',
+                                 'True', 'False', 'None')
+
+
+class Literal(Expr):
+    """Baseclass for literals."""
+    abstract = True
+
+
+class Const(Literal):
+    """All constant values.  The parser will return this node for simple
+    constants such as ``42`` or ``"foo"`` but it can be used to store more
+    complex values such as lists too.  Only constants with a safe
+    representation (objects where ``eval(repr(x)) == x`` is true).
+    """
+    fields = ('value',)
+
+    def as_const(self, eval_ctx=None):
+        return self.value
+
+    @classmethod
+    def from_untrusted(cls, value, lineno=None, environment=None):
+        """Return a const object if the value is representable as
+        constant value in the generated code, otherwise it will raise
+        an `Impossible` exception.
+        """
+        from .compiler import has_safe_repr
+        if not has_safe_repr(value):
+            raise Impossible()
+        return cls(value, lineno=lineno, environment=environment)
+
+
+class TemplateData(Literal):
+    """A constant template string."""
+    fields = ('data',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if eval_ctx.volatile:
+            raise Impossible()
+        if eval_ctx.autoescape:
+            return Markup(self.data)
+        return self.data
+
+
+class Tuple(Literal):
+    """For loop unpacking and some other things like multiple arguments
+    for subscripts.  Like for :class:`Name` `ctx` specifies if the tuple
+    is used for loading the names or storing.
+    """
+    fields = ('items', 'ctx')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return tuple(x.as_const(eval_ctx) for x in self.items)
+
+    def can_assign(self):
+        for item in self.items:
+            if not item.can_assign():
+                return False
+        return True
+
+
+class List(Literal):
+    """Any list literal such as ``[1, 2, 3]``"""
+    fields = ('items',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return [x.as_const(eval_ctx) for x in self.items]
+
+
+class Dict(Literal):
+    """Any dict literal such as ``{1: 2, 3: 4}``.  The items must be a list of
+    :class:`Pair` nodes.
+    """
+    fields = ('items',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return dict(x.as_const(eval_ctx) for x in self.items)
+
+
+class Pair(Helper):
+    """A key, value pair for dicts."""
+    fields = ('key', 'value')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return self.key.as_const(eval_ctx), self.value.as_const(eval_ctx)
+
+
+class Keyword(Helper):
+    """A key, value pair for keyword arguments where key is a string."""
+    fields = ('key', 'value')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return self.key, self.value.as_const(eval_ctx)
+
+
+class CondExpr(Expr):
+    """A conditional expression (inline if expression).  (``{{
+    foo if bar else baz }}``)
+    """
+    fields = ('test', 'expr1', 'expr2')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if self.test.as_const(eval_ctx):
+            return self.expr1.as_const(eval_ctx)
+
+        # if we evaluate to an undefined object, we better do that at runtime
+        if self.expr2 is None:
+            raise Impossible()
+
+        return self.expr2.as_const(eval_ctx)
+
+
+class Filter(Expr):
+    """This node applies a filter on an expression.  `name` is the name of
+    the filter, the rest of the fields are the same as for :class:`Call`.
+
+    If the `node` of a filter is `None` the contents of the last buffer are
+    filtered.  Buffers are created by macros and filter blocks.
+    """
+    fields = ('node', 'name', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if eval_ctx.volatile or self.node is None:
+            raise Impossible()
+        # we have to be careful here because we call filter_ below.
+        # if this variable would be called filter, 2to3 would wrap the
+        # call in a list beause it is assuming we are talking about the
+        # builtin filter function here which no longer returns a list in
+        # python 3.  because of that, do not rename filter_ to filter!
+        filter_ = self.environment.filters.get(self.name)
+        if filter_ is None or getattr(filter_, 'contextfilter', False):
+            raise Impossible()
+        obj = self.node.as_const(eval_ctx)
+        args = [x.as_const(eval_ctx) for x in self.args]
+        if getattr(filter_, 'evalcontextfilter', False):
+            args.insert(0, eval_ctx)
+        elif getattr(filter_, 'environmentfilter', False):
+            args.insert(0, self.environment)
+        kwargs = dict(x.as_const(eval_ctx) for x in self.kwargs)
+        if self.dyn_args is not None:
+            try:
+                args.extend(self.dyn_args.as_const(eval_ctx))
+            except Exception:
+                raise Impossible()
+        if self.dyn_kwargs is not None:
+            try:
+                kwargs.update(self.dyn_kwargs.as_const(eval_ctx))
+            except Exception:
+                raise Impossible()
+        try:
+            return filter_(obj, *args, **kwargs)
+        except Exception:
+            raise Impossible()
+
+
+class Test(Expr):
+    """Applies a test on an expression.  `name` is the name of the test, the
+    rest of the fields are the same as for :class:`Call`.
+    """
+    fields = ('node', 'name', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
+
+
+class Call(Expr):
+    """Calls an expression.  `args` is a list of arguments, `kwargs` a list
+    of keyword arguments (list of :class:`Keyword` nodes), and `dyn_args`
+    and `dyn_kwargs` has to be either `None` or a node that is used as
+    node for dynamic positional (``*args``) or keyword (``**kwargs``)
+    arguments.
+    """
+    fields = ('node', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if eval_ctx.volatile:
+            raise Impossible()
+        obj = self.node.as_const(eval_ctx)
+
+        # don't evaluate context functions
+        args = [x.as_const(eval_ctx) for x in self.args]
+        if isinstance(obj, _context_function_types):
+            if getattr(obj, 'contextfunction', False):
+                raise Impossible()
+            elif getattr(obj, 'evalcontextfunction', False):
+                args.insert(0, eval_ctx)
+            elif getattr(obj, 'environmentfunction', False):
+                args.insert(0, self.environment)
+
+        kwargs = dict(x.as_const(eval_ctx) for x in self.kwargs)
+        if self.dyn_args is not None:
+            try:
+                args.extend(self.dyn_args.as_const(eval_ctx))
+            except Exception:
+                raise Impossible()
+        if self.dyn_kwargs is not None:
+            try:
+                kwargs.update(self.dyn_kwargs.as_const(eval_ctx))
+            except Exception:
+                raise Impossible()
+        try:
+            return obj(*args, **kwargs)
+        except Exception:
+            raise Impossible()
+
+
+class Getitem(Expr):
+    """Get an attribute or item from an expression and prefer the item."""
+    fields = ('node', 'arg', 'ctx')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if self.ctx != 'load':
+            raise Impossible()
+        try:
+            return self.environment.getitem(self.node.as_const(eval_ctx),
+                                            self.arg.as_const(eval_ctx))
+        except Exception:
+            raise Impossible()
+
+    def can_assign(self):
+        return False
+
+
+class Getattr(Expr):
+    """Get an attribute or item from an expression that is a ascii-only
+    bytestring and prefer the attribute.
+    """
+    fields = ('node', 'attr', 'ctx')
+
+    def as_const(self, eval_ctx=None):
+        if self.ctx != 'load':
+            raise Impossible()
+        try:
+            eval_ctx = get_eval_context(self, eval_ctx)
+            return self.environment.getattr(self.node.as_const(eval_ctx),
+                                            self.attr)
+        except Exception:
+            raise Impossible()
+
+    def can_assign(self):
+        return False
+
+
+class Slice(Expr):
+    """Represents a slice object.  This must only be used as argument for
+    :class:`Subscript`.
+    """
+    fields = ('start', 'stop', 'step')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        def const(obj):
+            if obj is None:
+                return None
+            return obj.as_const(eval_ctx)
+        return slice(const(self.start), const(self.stop), const(self.step))
+
+
+class Concat(Expr):
+    """Concatenates the list of expressions provided after converting them to
+    unicode.
+    """
+    fields = ('nodes',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return ''.join(text_type(x.as_const(eval_ctx)) for x in self.nodes)
+
+
+class Compare(Expr):
+    """Compares an expression with some other expressions.  `ops` must be a
+    list of :class:`Operand`\s.
+    """
+    fields = ('expr', 'ops')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        result = value = self.expr.as_const(eval_ctx)
+        try:
+            for op in self.ops:
+                new_value = op.expr.as_const(eval_ctx)
+                result = _cmpop_to_func[op.op](value, new_value)
+                value = new_value
+        except Exception:
+            raise Impossible()
+        return result
+
+
+class Operand(Helper):
+    """Holds an operator and an expression."""
+    fields = ('op', 'expr')
+
+if __debug__:
+    Operand.__doc__ += '\nThe following operators are available: ' + \
+        ', '.join(sorted('``%s``' % x for x in set(_binop_to_func) |
+                  set(_uaop_to_func) | set(_cmpop_to_func)))
+
+
+class Mul(BinExpr):
+    """Multiplies the left with the right node."""
+    operator = '*'
+
+
+class Div(BinExpr):
+    """Divides the left by the right node."""
+    operator = '/'
+
+
+class FloorDiv(BinExpr):
+    """Divides the left by the right node and truncates conver the
+    result into an integer by truncating.
+    """
+    operator = '//'
+
+
+class Add(BinExpr):
+    """Add the left to the right node."""
+    operator = '+'
+
+
+class Sub(BinExpr):
+    """Subtract the right from the left node."""
+    operator = '-'
+
+
+class Mod(BinExpr):
+    """Left modulo right."""
+    operator = '%'
+
+
+class Pow(BinExpr):
+    """Left to the power of right."""
+    operator = '**'
+
+
+class And(BinExpr):
+    """Short circuited AND."""
+    operator = 'and'
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return self.left.as_const(eval_ctx) and self.right.as_const(eval_ctx)
+
+
+class Or(BinExpr):
+    """Short circuited OR."""
+    operator = 'or'
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return self.left.as_const(eval_ctx) or self.right.as_const(eval_ctx)
+
+
+class Not(UnaryExpr):
+    """Negate the expression."""
+    operator = 'not'
+
+
+class Neg(UnaryExpr):
+    """Make the expression negative."""
+    operator = '-'
+
+
+class Pos(UnaryExpr):
+    """Make the expression positive (noop for most expressions)"""
+    operator = '+'
+
+
+# Helpers for extensions
+
+
+class EnvironmentAttribute(Expr):
+    """Loads an attribute from the environment object.  This is useful for
+    extensions that want to call a callback stored on the environment.
+    """
+    fields = ('name',)
+
+
+class ExtensionAttribute(Expr):
+    """Returns the attribute of an extension bound to the environment.
+    The identifier is the identifier of the :class:`Extension`.
+
+    This node is usually constructed by calling the
+    :meth:`~jinja2.ext.Extension.attr` method on an extension.
+    """
+    fields = ('identifier', 'name')
+
+
+class ImportedName(Expr):
+    """If created with an import name the import name is returned on node
+    access.  For example ``ImportedName('cgi.escape')`` returns the `escape`
+    function from the cgi module on evaluation.  Imports are optimized by the
+    compiler so there is no need to assign them to local variables.
+    """
+    fields = ('importname',)
+
+
+class InternalName(Expr):
+    """An internal name in the compiler.  You cannot create these nodes
+    yourself but the parser provides a
+    :meth:`~jinja2.parser.Parser.free_identifier` method that creates
+    a new identifier for you.  This identifier is not available from the
+    template and is not threated specially by the compiler.
+    """
+    fields = ('name',)
+
+    def __init__(self):
+        raise TypeError('Can\'t create internal names.  Use the '
+                        '`free_identifier` method on a parser.')
+
+
+class MarkSafe(Expr):
+    """Mark the wrapped expression as safe (wrap it as `Markup`)."""
+    fields = ('expr',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return Markup(self.expr.as_const(eval_ctx))
+
+
+class MarkSafeIfAutoescape(Expr):
+    """Mark the wrapped expression as safe (wrap it as `Markup`) but
+    only if autoescaping is active.
+
+    .. versionadded:: 2.5
+    """
+    fields = ('expr',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if eval_ctx.volatile:
+            raise Impossible()
+        expr = self.expr.as_const(eval_ctx)
+        if eval_ctx.autoescape:
+            return Markup(expr)
+        return expr
+
+
+class ContextReference(Expr):
+    """Returns the current template context.  It can be used like a
+    :class:`Name` node, with a ``'load'`` ctx and will return the
+    current :class:`~jinja2.runtime.Context` object.
+
+    Here an example that assigns the current template name to a
+    variable named `foo`::
+
+        Assign(Name('foo', ctx='store'),
+               Getattr(ContextReference(), 'name'))
+    """
+
+
+class Continue(Stmt):
+    """Continue a loop."""
+
+
+class Break(Stmt):
+    """Break a loop."""
+
+
+class Scope(Stmt):
+    """An artificial scope."""
+    fields = ('body',)
+
+
+class EvalContextModifier(Stmt):
+    """Modifies the eval context.  For each option that should be modified,
+    a :class:`Keyword` has to be added to the :attr:`options` list.
+
+    Example to change the `autoescape` setting::
+
+        EvalContextModifier(options=[Keyword('autoescape', Const(True))])
+    """
+    fields = ('options',)
+
+
+class ScopedEvalContextModifier(EvalContextModifier):
+    """Modifies the eval context and reverts it later.  Works exactly like
+    :class:`EvalContextModifier` but will only modify the
+    :class:`~jinja2.nodes.EvalContext` for nodes in the :attr:`body`.
+    """
+    fields = ('body',)
+
+
+# make sure nobody creates custom nodes
+def _failing_new(*args, **kwargs):
+    raise TypeError('can\'t create custom node types')
+NodeType.__new__ = staticmethod(_failing_new); del _failing_new