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1# -*- coding: utf-8 -*-
2"""
3    jinja2.nodes
4    ~~~~~~~~~~~~
5
6    This module implements additional nodes derived from the ast base node.
7
8    It also provides some node tree helper functions like `in_lineno` and
9    `get_nodes` used by the parser and translator in order to normalize
10    python and jinja nodes.
11
12    :copyright: (c) 2017 by the Jinja Team.
13    :license: BSD, see LICENSE for more details.
14"""
15import types
16import operator
17
18from collections import deque
19from jinja2.utils import Markup
20from jinja2._compat import izip, with_metaclass, text_type, PY2
21
22
23#: the types we support for context functions
24_context_function_types = (types.FunctionType, types.MethodType)
25
26
27_binop_to_func = {
28    '*':        operator.mul,
29    '/':        operator.truediv,
30    '//':       operator.floordiv,
31    '**':       operator.pow,
32    '%':        operator.mod,
33    '+':        operator.add,
34    '-':        operator.sub
35}
36
37_uaop_to_func = {
38    'not':      operator.not_,
39    '+':        operator.pos,
40    '-':        operator.neg
41}
42
43_cmpop_to_func = {
44    'eq':       operator.eq,
45    'ne':       operator.ne,
46    'gt':       operator.gt,
47    'gteq':     operator.ge,
48    'lt':       operator.lt,
49    'lteq':     operator.le,
50    'in':       lambda a, b: a in b,
51    'notin':    lambda a, b: a not in b
52}
53
54
55class Impossible(Exception):
56    """Raised if the node could not perform a requested action."""
57
58
59class NodeType(type):
60    """A metaclass for nodes that handles the field and attribute
61    inheritance.  fields and attributes from the parent class are
62    automatically forwarded to the child."""
63
64    def __new__(cls, name, bases, d):
65        for attr in 'fields', 'attributes':
66            storage = []
67            storage.extend(getattr(bases[0], attr, ()))
68            storage.extend(d.get(attr, ()))
69            assert len(bases) == 1, 'multiple inheritance not allowed'
70            assert len(storage) == len(set(storage)), 'layout conflict'
71            d[attr] = tuple(storage)
72        d.setdefault('abstract', False)
73        return type.__new__(cls, name, bases, d)
74
75
76class EvalContext(object):
77    """Holds evaluation time information.  Custom attributes can be attached
78    to it in extensions.
79    """
80
81    def __init__(self, environment, template_name=None):
82        self.environment = environment
83        if callable(environment.autoescape):
84            self.autoescape = environment.autoescape(template_name)
85        else:
86            self.autoescape = environment.autoescape
87        self.volatile = False
88
89    def save(self):
90        return self.__dict__.copy()
91
92    def revert(self, old):
93        self.__dict__.clear()
94        self.__dict__.update(old)
95
96
97def get_eval_context(node, ctx):
98    if ctx is None:
99        if node.environment is None:
100            raise RuntimeError('if no eval context is passed, the '
101                               'node must have an attached '
102                               'environment.')
103        return EvalContext(node.environment)
104    return ctx
105
106
107class Node(with_metaclass(NodeType, object)):
108    """Baseclass for all Jinja2 nodes.  There are a number of nodes available
109    of different types.  There are four major types:
110
111    -   :class:`Stmt`: statements
112    -   :class:`Expr`: expressions
113    -   :class:`Helper`: helper nodes
114    -   :class:`Template`: the outermost wrapper node
115
116    All nodes have fields and attributes.  Fields may be other nodes, lists,
117    or arbitrary values.  Fields are passed to the constructor as regular
118    positional arguments, attributes as keyword arguments.  Each node has
119    two attributes: `lineno` (the line number of the node) and `environment`.
120    The `environment` attribute is set at the end of the parsing process for
121    all nodes automatically.
122    """
123    fields = ()
124    attributes = ('lineno', 'environment')
125    abstract = True
126
127    def __init__(self, *fields, **attributes):
128        if self.abstract:
129            raise TypeError('abstract nodes are not instanciable')
130        if fields:
131            if len(fields) != len(self.fields):
132                if not self.fields:
133                    raise TypeError('%r takes 0 arguments' %
134                                    self.__class__.__name__)
135                raise TypeError('%r takes 0 or %d argument%s' % (
136                    self.__class__.__name__,
137                    len(self.fields),
138                    len(self.fields) != 1 and 's' or ''
139                ))
140            for name, arg in izip(self.fields, fields):
141                setattr(self, name, arg)
142        for attr in self.attributes:
143            setattr(self, attr, attributes.pop(attr, None))
144        if attributes:
145            raise TypeError('unknown attribute %r' %
146                            next(iter(attributes)))
147
148    def iter_fields(self, exclude=None, only=None):
149        """This method iterates over all fields that are defined and yields
150        ``(key, value)`` tuples.  Per default all fields are returned, but
151        it's possible to limit that to some fields by providing the `only`
152        parameter or to exclude some using the `exclude` parameter.  Both
153        should be sets or tuples of field names.
154        """
155        for name in self.fields:
156            if (exclude is only is None) or \
157               (exclude is not None and name not in exclude) or \
158               (only is not None and name in only):
159                try:
160                    yield name, getattr(self, name)
161                except AttributeError:
162                    pass
163
164    def iter_child_nodes(self, exclude=None, only=None):
165        """Iterates over all direct child nodes of the node.  This iterates
166        over all fields and yields the values of they are nodes.  If the value
167        of a field is a list all the nodes in that list are returned.
168        """
169        for field, item in self.iter_fields(exclude, only):
170            if isinstance(item, list):
171                for n in item:
172                    if isinstance(n, Node):
173                        yield n
174            elif isinstance(item, Node):
175                yield item
176
177    def find(self, node_type):
178        """Find the first node of a given type.  If no such node exists the
179        return value is `None`.
180        """
181        for result in self.find_all(node_type):
182            return result
183
184    def find_all(self, node_type):
185        """Find all the nodes of a given type.  If the type is a tuple,
186        the check is performed for any of the tuple items.
187        """
188        for child in self.iter_child_nodes():
189            if isinstance(child, node_type):
190                yield child
191            for result in child.find_all(node_type):
192                yield result
193
194    def set_ctx(self, ctx):
195        """Reset the context of a node and all child nodes.  Per default the
196        parser will all generate nodes that have a 'load' context as it's the
197        most common one.  This method is used in the parser to set assignment
198        targets and other nodes to a store context.
199        """
200        todo = deque([self])
201        while todo:
202            node = todo.popleft()
203            if 'ctx' in node.fields:
204                node.ctx = ctx
205            todo.extend(node.iter_child_nodes())
206        return self
207
208    def set_lineno(self, lineno, override=False):
209        """Set the line numbers of the node and children."""
210        todo = deque([self])
211        while todo:
212            node = todo.popleft()
213            if 'lineno' in node.attributes:
214                if node.lineno is None or override:
215                    node.lineno = lineno
216            todo.extend(node.iter_child_nodes())
217        return self
218
219    def set_environment(self, environment):
220        """Set the environment for all nodes."""
221        todo = deque([self])
222        while todo:
223            node = todo.popleft()
224            node.environment = environment
225            todo.extend(node.iter_child_nodes())
226        return self
227
228    def __eq__(self, other):
229        return type(self) is type(other) and \
230               tuple(self.iter_fields()) == tuple(other.iter_fields())
231
232    def __ne__(self, other):
233        return not self.__eq__(other)
234
235    # Restore Python 2 hashing behavior on Python 3
236    __hash__ = object.__hash__
237
238    def __repr__(self):
239        return '%s(%s)' % (
240            self.__class__.__name__,
241            ', '.join('%s=%r' % (arg, getattr(self, arg, None)) for
242                      arg in self.fields)
243        )
244
245    def dump(self):
246        def _dump(node):
247            if not isinstance(node, Node):
248                buf.append(repr(node))
249                return
250
251            buf.append('nodes.%s(' % node.__class__.__name__)
252            if not node.fields:
253                buf.append(')')
254                return
255            for idx, field in enumerate(node.fields):
256                if idx:
257                    buf.append(', ')
258                value = getattr(node, field)
259                if isinstance(value, list):
260                    buf.append('[')
261                    for idx, item in enumerate(value):
262                        if idx:
263                            buf.append(', ')
264                        _dump(item)
265                    buf.append(']')
266                else:
267                    _dump(value)
268            buf.append(')')
269        buf = []
270        _dump(self)
271        return ''.join(buf)
272
273
274
275class Stmt(Node):
276    """Base node for all statements."""
277    abstract = True
278
279
280class Helper(Node):
281    """Nodes that exist in a specific context only."""
282    abstract = True
283
284
285class Template(Node):
286    """Node that represents a template.  This must be the outermost node that
287    is passed to the compiler.
288    """
289    fields = ('body',)
290
291
292class Output(Stmt):
293    """A node that holds multiple expressions which are then printed out.
294    This is used both for the `print` statement and the regular template data.
295    """
296    fields = ('nodes',)
297
298
299class Extends(Stmt):
300    """Represents an extends statement."""
301    fields = ('template',)
302
303
304class For(Stmt):
305    """The for loop.  `target` is the target for the iteration (usually a
306    :class:`Name` or :class:`Tuple`), `iter` the iterable.  `body` is a list
307    of nodes that are used as loop-body, and `else_` a list of nodes for the
308    `else` block.  If no else node exists it has to be an empty list.
309
310    For filtered nodes an expression can be stored as `test`, otherwise `None`.
311    """
312    fields = ('target', 'iter', 'body', 'else_', 'test', 'recursive')
313
314
315class If(Stmt):
316    """If `test` is true, `body` is rendered, else `else_`."""
317    fields = ('test', 'body', 'elif_', 'else_')
318
319
320class Macro(Stmt):
321    """A macro definition.  `name` is the name of the macro, `args` a list of
322    arguments and `defaults` a list of defaults if there are any.  `body` is
323    a list of nodes for the macro body.
324    """
325    fields = ('name', 'args', 'defaults', 'body')
326
327
328class CallBlock(Stmt):
329    """Like a macro without a name but a call instead.  `call` is called with
330    the unnamed macro as `caller` argument this node holds.
331    """
332    fields = ('call', 'args', 'defaults', 'body')
333
334
335class FilterBlock(Stmt):
336    """Node for filter sections."""
337    fields = ('body', 'filter')
338
339
340class With(Stmt):
341    """Specific node for with statements.  In older versions of Jinja the
342    with statement was implemented on the base of the `Scope` node instead.
343
344    .. versionadded:: 2.9.3
345    """
346    fields = ('targets', 'values', 'body')
347
348
349class Block(Stmt):
350    """A node that represents a block."""
351    fields = ('name', 'body', 'scoped')
352
353
354class Include(Stmt):
355    """A node that represents the include tag."""
356    fields = ('template', 'with_context', 'ignore_missing')
357
358
359class Import(Stmt):
360    """A node that represents the import tag."""
361    fields = ('template', 'target', 'with_context')
362
363
364class FromImport(Stmt):
365    """A node that represents the from import tag.  It's important to not
366    pass unsafe names to the name attribute.  The compiler translates the
367    attribute lookups directly into getattr calls and does *not* use the
368    subscript callback of the interface.  As exported variables may not
369    start with double underscores (which the parser asserts) this is not a
370    problem for regular Jinja code, but if this node is used in an extension
371    extra care must be taken.
372
373    The list of names may contain tuples if aliases are wanted.
374    """
375    fields = ('template', 'names', 'with_context')
376
377
378class ExprStmt(Stmt):
379    """A statement that evaluates an expression and discards the result."""
380    fields = ('node',)
381
382
383class Assign(Stmt):
384    """Assigns an expression to a target."""
385    fields = ('target', 'node')
386
387
388class AssignBlock(Stmt):
389    """Assigns a block to a target."""
390    fields = ('target', 'filter', 'body')
391
392
393class Expr(Node):
394    """Baseclass for all expressions."""
395    abstract = True
396
397    def as_const(self, eval_ctx=None):
398        """Return the value of the expression as constant or raise
399        :exc:`Impossible` if this was not possible.
400
401        An :class:`EvalContext` can be provided, if none is given
402        a default context is created which requires the nodes to have
403        an attached environment.
404
405        .. versionchanged:: 2.4
406           the `eval_ctx` parameter was added.
407        """
408        raise Impossible()
409
410    def can_assign(self):
411        """Check if it's possible to assign something to this node."""
412        return False
413
414
415class BinExpr(Expr):
416    """Baseclass for all binary expressions."""
417    fields = ('left', 'right')
418    operator = None
419    abstract = True
420
421    def as_const(self, eval_ctx=None):
422        eval_ctx = get_eval_context(self, eval_ctx)
423        # intercepted operators cannot be folded at compile time
424        if self.environment.sandboxed and \
425           self.operator in self.environment.intercepted_binops:
426            raise Impossible()
427        f = _binop_to_func[self.operator]
428        try:
429            return f(self.left.as_const(eval_ctx), self.right.as_const(eval_ctx))
430        except Exception:
431            raise Impossible()
432
433
434class UnaryExpr(Expr):
435    """Baseclass for all unary expressions."""
436    fields = ('node',)
437    operator = None
438    abstract = True
439
440    def as_const(self, eval_ctx=None):
441        eval_ctx = get_eval_context(self, eval_ctx)
442        # intercepted operators cannot be folded at compile time
443        if self.environment.sandboxed and \
444           self.operator in self.environment.intercepted_unops:
445            raise Impossible()
446        f = _uaop_to_func[self.operator]
447        try:
448            return f(self.node.as_const(eval_ctx))
449        except Exception:
450            raise Impossible()
451
452
453class Name(Expr):
454    """Looks up a name or stores a value in a name.
455    The `ctx` of the node can be one of the following values:
456
457    -   `store`: store a value in the name
458    -   `load`: load that name
459    -   `param`: like `store` but if the name was defined as function parameter.
460    """
461    fields = ('name', 'ctx')
462
463    def can_assign(self):
464        return self.name not in ('true', 'false', 'none',
465                                 'True', 'False', 'None')
466
467
468class NSRef(Expr):
469    """Reference to a namespace value assignment"""
470    fields = ('name', 'attr')
471
472    def can_assign(self):
473        # We don't need any special checks here; NSRef assignments have a
474        # runtime check to ensure the target is a namespace object which will
475        # have been checked already as it is created using a normal assignment
476        # which goes through a `Name` node.
477        return True
478
479
480class Literal(Expr):
481    """Baseclass for literals."""
482    abstract = True
483
484
485class Const(Literal):
486    """All constant values.  The parser will return this node for simple
487    constants such as ``42`` or ``"foo"`` but it can be used to store more
488    complex values such as lists too.  Only constants with a safe
489    representation (objects where ``eval(repr(x)) == x`` is true).
490    """
491    fields = ('value',)
492
493    def as_const(self, eval_ctx=None):
494        rv = self.value
495        if PY2 and type(rv) is text_type and \
496           self.environment.policies['compiler.ascii_str']:
497            try:
498                rv = rv.encode('ascii')
499            except UnicodeError:
500                pass
501        return rv
502
503    @classmethod
504    def from_untrusted(cls, value, lineno=None, environment=None):
505        """Return a const object if the value is representable as
506        constant value in the generated code, otherwise it will raise
507        an `Impossible` exception.
508        """
509        from .compiler import has_safe_repr
510        if not has_safe_repr(value):
511            raise Impossible()
512        return cls(value, lineno=lineno, environment=environment)
513
514
515class TemplateData(Literal):
516    """A constant template string."""
517    fields = ('data',)
518
519    def as_const(self, eval_ctx=None):
520        eval_ctx = get_eval_context(self, eval_ctx)
521        if eval_ctx.volatile:
522            raise Impossible()
523        if eval_ctx.autoescape:
524            return Markup(self.data)
525        return self.data
526
527
528class Tuple(Literal):
529    """For loop unpacking and some other things like multiple arguments
530    for subscripts.  Like for :class:`Name` `ctx` specifies if the tuple
531    is used for loading the names or storing.
532    """
533    fields = ('items', 'ctx')
534
535    def as_const(self, eval_ctx=None):
536        eval_ctx = get_eval_context(self, eval_ctx)
537        return tuple(x.as_const(eval_ctx) for x in self.items)
538
539    def can_assign(self):
540        for item in self.items:
541            if not item.can_assign():
542                return False
543        return True
544
545
546class List(Literal):
547    """Any list literal such as ``[1, 2, 3]``"""
548    fields = ('items',)
549
550    def as_const(self, eval_ctx=None):
551        eval_ctx = get_eval_context(self, eval_ctx)
552        return [x.as_const(eval_ctx) for x in self.items]
553
554
555class Dict(Literal):
556    """Any dict literal such as ``{1: 2, 3: 4}``.  The items must be a list of
557    :class:`Pair` nodes.
558    """
559    fields = ('items',)
560
561    def as_const(self, eval_ctx=None):
562        eval_ctx = get_eval_context(self, eval_ctx)
563        return dict(x.as_const(eval_ctx) for x in self.items)
564
565
566class Pair(Helper):
567    """A key, value pair for dicts."""
568    fields = ('key', 'value')
569
570    def as_const(self, eval_ctx=None):
571        eval_ctx = get_eval_context(self, eval_ctx)
572        return self.key.as_const(eval_ctx), self.value.as_const(eval_ctx)
573
574
575class Keyword(Helper):
576    """A key, value pair for keyword arguments where key is a string."""
577    fields = ('key', 'value')
578
579    def as_const(self, eval_ctx=None):
580        eval_ctx = get_eval_context(self, eval_ctx)
581        return self.key, self.value.as_const(eval_ctx)
582
583
584class CondExpr(Expr):
585    """A conditional expression (inline if expression).  (``{{
586    foo if bar else baz }}``)
587    """
588    fields = ('test', 'expr1', 'expr2')
589
590    def as_const(self, eval_ctx=None):
591        eval_ctx = get_eval_context(self, eval_ctx)
592        if self.test.as_const(eval_ctx):
593            return self.expr1.as_const(eval_ctx)
594
595        # if we evaluate to an undefined object, we better do that at runtime
596        if self.expr2 is None:
597            raise Impossible()
598
599        return self.expr2.as_const(eval_ctx)
600
601
602def args_as_const(node, eval_ctx):
603    args = [x.as_const(eval_ctx) for x in node.args]
604    kwargs = dict(x.as_const(eval_ctx) for x in node.kwargs)
605
606    if node.dyn_args is not None:
607        try:
608            args.extend(node.dyn_args.as_const(eval_ctx))
609        except Exception:
610            raise Impossible()
611
612    if node.dyn_kwargs is not None:
613        try:
614            kwargs.update(node.dyn_kwargs.as_const(eval_ctx))
615        except Exception:
616            raise Impossible()
617
618    return args, kwargs
619
620
621class Filter(Expr):
622    """This node applies a filter on an expression.  `name` is the name of
623    the filter, the rest of the fields are the same as for :class:`Call`.
624
625    If the `node` of a filter is `None` the contents of the last buffer are
626    filtered.  Buffers are created by macros and filter blocks.
627    """
628
629    fields = ('node', 'name', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
630
631    def as_const(self, eval_ctx=None):
632        eval_ctx = get_eval_context(self, eval_ctx)
633
634        if eval_ctx.volatile or self.node is None:
635            raise Impossible()
636
637        # we have to be careful here because we call filter_ below.
638        # if this variable would be called filter, 2to3 would wrap the
639        # call in a list beause it is assuming we are talking about the
640        # builtin filter function here which no longer returns a list in
641        # python 3.  because of that, do not rename filter_ to filter!
642        filter_ = self.environment.filters.get(self.name)
643
644        if filter_ is None or getattr(filter_, 'contextfilter', False):
645            raise Impossible()
646
647        # We cannot constant handle async filters, so we need to make sure
648        # to not go down this path.
649        if (
650            eval_ctx.environment.is_async
651            and getattr(filter_, 'asyncfiltervariant', False)
652        ):
653            raise Impossible()
654
655        args, kwargs = args_as_const(self, eval_ctx)
656        args.insert(0, self.node.as_const(eval_ctx))
657
658        if getattr(filter_, 'evalcontextfilter', False):
659            args.insert(0, eval_ctx)
660        elif getattr(filter_, 'environmentfilter', False):
661            args.insert(0, self.environment)
662
663        try:
664            return filter_(*args, **kwargs)
665        except Exception:
666            raise Impossible()
667
668
669class Test(Expr):
670    """Applies a test on an expression.  `name` is the name of the test, the
671    rest of the fields are the same as for :class:`Call`.
672    """
673
674    fields = ('node', 'name', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
675
676    def as_const(self, eval_ctx=None):
677        test = self.environment.tests.get(self.name)
678
679        if test is None:
680            raise Impossible()
681
682        eval_ctx = get_eval_context(self, eval_ctx)
683        args, kwargs = args_as_const(self, eval_ctx)
684        args.insert(0, self.node.as_const(eval_ctx))
685
686        try:
687            return test(*args, **kwargs)
688        except Exception:
689            raise Impossible()
690
691
692class Call(Expr):
693    """Calls an expression.  `args` is a list of arguments, `kwargs` a list
694    of keyword arguments (list of :class:`Keyword` nodes), and `dyn_args`
695    and `dyn_kwargs` has to be either `None` or a node that is used as
696    node for dynamic positional (``*args``) or keyword (``**kwargs``)
697    arguments.
698    """
699    fields = ('node', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
700
701
702class Getitem(Expr):
703    """Get an attribute or item from an expression and prefer the item."""
704    fields = ('node', 'arg', 'ctx')
705
706    def as_const(self, eval_ctx=None):
707        eval_ctx = get_eval_context(self, eval_ctx)
708        if self.ctx != 'load':
709            raise Impossible()
710        try:
711            return self.environment.getitem(self.node.as_const(eval_ctx),
712                                            self.arg.as_const(eval_ctx))
713        except Exception:
714            raise Impossible()
715
716    def can_assign(self):
717        return False
718
719
720class Getattr(Expr):
721    """Get an attribute or item from an expression that is a ascii-only
722    bytestring and prefer the attribute.
723    """
724    fields = ('node', 'attr', 'ctx')
725
726    def as_const(self, eval_ctx=None):
727        if self.ctx != 'load':
728            raise Impossible()
729        try:
730            eval_ctx = get_eval_context(self, eval_ctx)
731            return self.environment.getattr(self.node.as_const(eval_ctx),
732                                            self.attr)
733        except Exception:
734            raise Impossible()
735
736    def can_assign(self):
737        return False
738
739
740class Slice(Expr):
741    """Represents a slice object.  This must only be used as argument for
742    :class:`Subscript`.
743    """
744    fields = ('start', 'stop', 'step')
745
746    def as_const(self, eval_ctx=None):
747        eval_ctx = get_eval_context(self, eval_ctx)
748        def const(obj):
749            if obj is None:
750                return None
751            return obj.as_const(eval_ctx)
752        return slice(const(self.start), const(self.stop), const(self.step))
753
754
755class Concat(Expr):
756    """Concatenates the list of expressions provided after converting them to
757    unicode.
758    """
759    fields = ('nodes',)
760
761    def as_const(self, eval_ctx=None):
762        eval_ctx = get_eval_context(self, eval_ctx)
763        return ''.join(text_type(x.as_const(eval_ctx)) for x in self.nodes)
764
765
766class Compare(Expr):
767    """Compares an expression with some other expressions.  `ops` must be a
768    list of :class:`Operand`\\s.
769    """
770    fields = ('expr', 'ops')
771
772    def as_const(self, eval_ctx=None):
773        eval_ctx = get_eval_context(self, eval_ctx)
774        result = value = self.expr.as_const(eval_ctx)
775        try:
776            for op in self.ops:
777                new_value = op.expr.as_const(eval_ctx)
778                result = _cmpop_to_func[op.op](value, new_value)
779                value = new_value
780        except Exception:
781            raise Impossible()
782        return result
783
784
785class Operand(Helper):
786    """Holds an operator and an expression."""
787    fields = ('op', 'expr')
788
789if __debug__:
790    Operand.__doc__ += '\nThe following operators are available: ' + \
791        ', '.join(sorted('``%s``' % x for x in set(_binop_to_func) |
792                  set(_uaop_to_func) | set(_cmpop_to_func)))
793
794
795class Mul(BinExpr):
796    """Multiplies the left with the right node."""
797    operator = '*'
798
799
800class Div(BinExpr):
801    """Divides the left by the right node."""
802    operator = '/'
803
804
805class FloorDiv(BinExpr):
806    """Divides the left by the right node and truncates conver the
807    result into an integer by truncating.
808    """
809    operator = '//'
810
811
812class Add(BinExpr):
813    """Add the left to the right node."""
814    operator = '+'
815
816
817class Sub(BinExpr):
818    """Subtract the right from the left node."""
819    operator = '-'
820
821
822class Mod(BinExpr):
823    """Left modulo right."""
824    operator = '%'
825
826
827class Pow(BinExpr):
828    """Left to the power of right."""
829    operator = '**'
830
831
832class And(BinExpr):
833    """Short circuited AND."""
834    operator = 'and'
835
836    def as_const(self, eval_ctx=None):
837        eval_ctx = get_eval_context(self, eval_ctx)
838        return self.left.as_const(eval_ctx) and self.right.as_const(eval_ctx)
839
840
841class Or(BinExpr):
842    """Short circuited OR."""
843    operator = 'or'
844
845    def as_const(self, eval_ctx=None):
846        eval_ctx = get_eval_context(self, eval_ctx)
847        return self.left.as_const(eval_ctx) or self.right.as_const(eval_ctx)
848
849
850class Not(UnaryExpr):
851    """Negate the expression."""
852    operator = 'not'
853
854
855class Neg(UnaryExpr):
856    """Make the expression negative."""
857    operator = '-'
858
859
860class Pos(UnaryExpr):
861    """Make the expression positive (noop for most expressions)"""
862    operator = '+'
863
864
865# Helpers for extensions
866
867
868class EnvironmentAttribute(Expr):
869    """Loads an attribute from the environment object.  This is useful for
870    extensions that want to call a callback stored on the environment.
871    """
872    fields = ('name',)
873
874
875class ExtensionAttribute(Expr):
876    """Returns the attribute of an extension bound to the environment.
877    The identifier is the identifier of the :class:`Extension`.
878
879    This node is usually constructed by calling the
880    :meth:`~jinja2.ext.Extension.attr` method on an extension.
881    """
882    fields = ('identifier', 'name')
883
884
885class ImportedName(Expr):
886    """If created with an import name the import name is returned on node
887    access.  For example ``ImportedName('cgi.escape')`` returns the `escape`
888    function from the cgi module on evaluation.  Imports are optimized by the
889    compiler so there is no need to assign them to local variables.
890    """
891    fields = ('importname',)
892
893
894class InternalName(Expr):
895    """An internal name in the compiler.  You cannot create these nodes
896    yourself but the parser provides a
897    :meth:`~jinja2.parser.Parser.free_identifier` method that creates
898    a new identifier for you.  This identifier is not available from the
899    template and is not threated specially by the compiler.
900    """
901    fields = ('name',)
902
903    def __init__(self):
904        raise TypeError('Can\'t create internal names.  Use the '
905                        '`free_identifier` method on a parser.')
906
907
908class MarkSafe(Expr):
909    """Mark the wrapped expression as safe (wrap it as `Markup`)."""
910    fields = ('expr',)
911
912    def as_const(self, eval_ctx=None):
913        eval_ctx = get_eval_context(self, eval_ctx)
914        return Markup(self.expr.as_const(eval_ctx))
915
916
917class MarkSafeIfAutoescape(Expr):
918    """Mark the wrapped expression as safe (wrap it as `Markup`) but
919    only if autoescaping is active.
920
921    .. versionadded:: 2.5
922    """
923    fields = ('expr',)
924
925    def as_const(self, eval_ctx=None):
926        eval_ctx = get_eval_context(self, eval_ctx)
927        if eval_ctx.volatile:
928            raise Impossible()
929        expr = self.expr.as_const(eval_ctx)
930        if eval_ctx.autoescape:
931            return Markup(expr)
932        return expr
933
934
935class ContextReference(Expr):
936    """Returns the current template context.  It can be used like a
937    :class:`Name` node, with a ``'load'`` ctx and will return the
938    current :class:`~jinja2.runtime.Context` object.
939
940    Here an example that assigns the current template name to a
941    variable named `foo`::
942
943        Assign(Name('foo', ctx='store'),
944               Getattr(ContextReference(), 'name'))
945    """
946
947
948class Continue(Stmt):
949    """Continue a loop."""
950
951
952class Break(Stmt):
953    """Break a loop."""
954
955
956class Scope(Stmt):
957    """An artificial scope."""
958    fields = ('body',)
959
960
961class OverlayScope(Stmt):
962    """An overlay scope for extensions.  This is a largely unoptimized scope
963    that however can be used to introduce completely arbitrary variables into
964    a sub scope from a dictionary or dictionary like object.  The `context`
965    field has to evaluate to a dictionary object.
966
967    Example usage::
968
969        OverlayScope(context=self.call_method('get_context'),
970                     body=[...])
971
972    .. versionadded:: 2.10
973    """
974    fields = ('context', 'body')
975
976
977class EvalContextModifier(Stmt):
978    """Modifies the eval context.  For each option that should be modified,
979    a :class:`Keyword` has to be added to the :attr:`options` list.
980
981    Example to change the `autoescape` setting::
982
983        EvalContextModifier(options=[Keyword('autoescape', Const(True))])
984    """
985    fields = ('options',)
986
987
988class ScopedEvalContextModifier(EvalContextModifier):
989    """Modifies the eval context and reverts it later.  Works exactly like
990    :class:`EvalContextModifier` but will only modify the
991    :class:`~jinja2.nodes.EvalContext` for nodes in the :attr:`body`.
992    """
993    fields = ('body',)
994
995
996# make sure nobody creates custom nodes
997def _failing_new(*args, **kwargs):
998    raise TypeError('can\'t create custom node types')
999NodeType.__new__ = staticmethod(_failing_new); del _failing_new
1000