jinja2/nodes.py

# -*- 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: 2008 by Armin Ronacher.
    :license: BSD, see LICENSE for more details.
"""
import operator
from types import FunctionType
from itertools import chain, izip
from collections import deque
from copy import copy


_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)
        return type.__new__(cls, name, bases, d)


class Node(object):
    """Baseclass for all Jinja nodes."""
    __metaclass__ = NodeType
    fields = ()
    attributes = ('lineno', 'environment')

    def __init__(self, *args, **kw):
        if args:
            if len(args) != 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, args):
                setattr(self, name, arg)
        for attr in self.attributes:
            setattr(self, attr, kw.pop(attr, None))
        if kw:
            raise TypeError('unknown keyword argument %r' %
                            iter(kw).next())

    def iter_fields(self, exclude=()):
        """Iterate over all fields."""
        for name in self.fields:
            if name not in exclude:
                try:
                    yield name, getattr(self, name)
                except AttributeError:
                    pass

    def iter_child_nodes(self, exclude=()):
        """Iterate over all child nodes."""
        for field, item in self.iter_fields(exclude):
            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."""
        for result in self.find_all(node_type):
            return result

    def find_all(self, node_type):
        """Find all the nodes of a given type."""
        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 copy(self):
        """Return a deep copy of the node."""
        result = object.__new__(self.__class__)
        for field, value in self.iter_fields():
            if isinstance(value, Node):
                new_value = value.copy()
            elif isinstance(value, list):
                new_value = []
                for item in value:
                    if isinstance(item, Node):
                        item = item.copy()
                    else:
                        item = copy(item)
                    new_value.append(item)
            else:
                new_value = copy(value)
            setattr(result, field, new_value)
        for attr in self.attributes:
            try:
                setattr(result, attr, getattr(self, attr))
            except AttributeError:
                pass
        return 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())

    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())

    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())

    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."""


class Helper(Node):
    """Nodes that exist in a specific context only."""


class Template(Node):
    """Node that represents a template."""
    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',)

    def optimized_nodes(self):
        """Try to optimize the nodes."""
        buffer = []
        for node in self.nodes:
            try:
                const = unicode(node.as_const())
            except:
                buffer.append(node)
            else:
                if buffer and isinstance(buffer[-1], unicode):
                    buffer[-1] += const
                else:
                    buffer.append(const)
        return buffer


class Extends(Stmt):
    """Represents an extends statement."""
    fields = ('template',)


class For(Stmt):
    """A node that represents a for loop"""
    fields = ('target', 'iter', 'body', 'else_', 'test')


class If(Stmt):
    """A node that represents an if condition."""
    fields = ('test', 'body', 'else_')


class Macro(Stmt):
    """A node that represents a macro."""
    fields = ('name', 'args', 'defaults', 'body')


class CallBlock(Stmt):
    """A node that represents am extended macro call."""
    fields = ('call', 'args', 'defaults', 'body')


class Set(Stmt):
    """Allows defining own variables."""
    fields = ('name', 'expr')


class FilterBlock(Stmt):
    """Node for filter sections."""
    fields = ('body', 'filter')


class Block(Stmt):
    """A node that represents a block."""
    fields = ('name', 'body')


class Include(Stmt):
    """A node that represents the include tag."""
    fields = ('template',)


class Import(Stmt):
    """A node that represents the import tag."""
    fields = ('template', 'target')


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
    subscribe 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')


class Trans(Stmt):
    """A node for translatable sections."""
    fields = ('singular', 'plural', 'indicator', 'replacements')


class ExprStmt(Stmt):
    """A statement that evaluates an expression to None."""
    fields = ('node',)


class Assign(Stmt):
    """Assigns an expression to a target."""
    fields = ('target', 'node')


class Expr(Node):
    """Baseclass for all expressions."""

    def as_const(self):
        """Return the value of the expression as constant or raise
        `Impossible` if this was not possible.
        """
        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

    def as_const(self):
        f = _binop_to_func[self.operator]
        try:
            return f(self.left.as_const(), self.right.as_const())
        except:
            raise Impossible()


class UnaryExpr(Expr):
    """Baseclass for all unary expressions."""
    fields = ('node',)
    operator = None

    def as_const(self):
        f = _uaop_to_func[self.operator]
        try:
            return f(self.node.as_const())
        except:
            raise Impossible()


class Name(Expr):
    """any name such as {{ foo }}"""
    fields = ('name', 'ctx')

    def can_assign(self):
        return self.name not in ('true', 'false', 'none')


class Literal(Expr):
    """Baseclass for literals."""


class Const(Literal):
    """any constat such as {{ "foo" }}"""
    fields = ('value',)

    def as_const(self):
        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 Tuple(Literal):
    """For loop unpacking and some other things like multiple arguments
    for subscripts.
    """
    fields = ('items', 'ctx')

    def as_const(self):
        return tuple(x.as_const() 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):
        return [x.as_const() for x in self.items]


class Dict(Literal):
    """any dict literal such as {{ {1: 2, 3: 4} }}"""
    fields = ('items',)

    def as_const(self):
        return dict(x.as_const() for x in self.items)


class Pair(Helper):
    """A key, value pair for dicts."""
    fields = ('key', 'value')

    def as_const(self):
        return self.key.as_const(), self.value.as_const()


class Keyword(Helper):
    """A key, value pair for keyword arguments."""
    fields = ('key', 'value')


class CondExpr(Expr):
    """{{ foo if bar else baz }}"""
    fields = ('test', 'expr1', 'expr2')

    def as_const(self):
        if self.test.as_const():
            return self.expr1.as_const()
        return self.expr2.as_const()


class Filter(Expr):
    """{{ foo|bar|baz }}"""
    fields = ('node', 'name', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')

    def as_const(self, obj=None):
        if self.node is obj is None:
            raise Impossible()
        filter = self.environment.filters.get(self.name)
        if filter is None or getattr(filter, 'contextfilter', False):
            raise Impossible()
        if obj is None:
            obj = self.node.as_const()
        args = [x.as_const() for x in self.args]
        if getattr(filter, 'environmentfilter', False):
            args.insert(0, self.environment)
        kwargs = dict(x.as_const() for x in self.kwargs)
        if self.dyn_args is not None:
            try:
                args.extend(self.dyn_args.as_const())
            except:
                raise Impossible()
        if self.dyn_kwargs is not None:
            try:
                kwargs.update(self.dyn_kwargs.as_const())
            except:
                raise Impossible()
        try:
            return filter(obj, *args, **kwargs)
        except:
            raise Impossible()


class Test(Expr):
    """{{ foo is lower }}"""
    fields = ('node', 'name', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')


class Call(Expr):
    """{{ foo(bar) }}"""
    fields = ('node', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')

    def as_const(self):
        obj = self.node.as_const()

        # don't evaluate context functions
        args = [x.as_const() for x in self.args]
        if type(obj) is FunctionType:
            if getattr(obj, 'contextfunction', False):
                raise Impossible()
            elif obj.environmentfunction:
                args.insert(0, self.environment)

        kwargs = dict(x.as_const() for x in self.kwargs)
        if self.dyn_args is not None:
            try:
                args.extend(self.dyn_args.as_const())
            except:
                raise Impossible()
        if self.dyn_kwargs is not None:
            try:
                kwargs.update(self.dyn_kwargs.as_const())
            except:
                raise Impossible()
        try:
            return obj(*args, **kwargs)
        except:
            raise Impossible()


class Subscript(Expr):
    """{{ foo.bar }} and {{ foo['bar'] }} etc."""
    fields = ('node', 'arg', 'ctx')

    def as_const(self):
        if self.ctx != 'load':
            raise Impossible()
        try:
            return self.environment.subscribe(self.node.as_const(),
                                              self.arg.as_const())
        except:
            raise Impossible()

    def can_assign(self):
        return False


class Slice(Expr):
    """1:2:3 etc."""
    fields = ('start', 'stop', 'step')

    def as_const(self):
        def const(obj):
            if obj is None:
                return obj
            return obj.as_const()
        return slice(const(self.start), const(self.stop), const(self.step))


class Concat(Expr):
    """For {{ foo ~ bar }}.  Concatenates strings."""
    fields = ('nodes',)

    def as_const(self):
        return ''.join(unicode(x.as_const()) for x in self.nodes)


class Compare(Expr):
    """{{ foo == bar }}, {{ foo >= bar }} etc."""
    fields = ('expr', 'ops')

    def as_const(self):
        result = value = self.expr.as_const()
        try:
            for op in self.ops:
                new_value = op.expr.as_const()
                result = _cmpop_to_func[op.op](value, new_value)
                value = new_value
        except:
            raise Impossible()
        return result


class Operand(Helper):
    """Operator + expression."""
    fields = ('op', 'expr')


class Mul(BinExpr):
    """{{ foo * bar }}"""
    operator = '*'


class Div(BinExpr):
    """{{ foo / bar }}"""
    operator = '/'


class FloorDiv(BinExpr):
    """{{ foo // bar }}"""
    operator = '//'


class Add(BinExpr):
    """{{ foo + bar }}"""
    operator = '+'


class Sub(BinExpr):
    """{{ foo - bar }}"""
    operator = '-'


class Mod(BinExpr):
    """{{ foo % bar }}"""
    operator = '%'


class Pow(BinExpr):
    """{{ foo ** bar }}"""
    operator = '**'


class And(BinExpr):
    """{{ foo and bar }}"""
    operator = 'and'

    def as_const(self):
        return self.left.as_const() and self.right.as_const()


class Or(BinExpr):
    """{{ foo or bar }}"""
    operator = 'or'

    def as_const(self):
        return self.left.as_const() or self.right.as_const()


class Not(UnaryExpr):
    """{{ not foo }}"""
    operator = 'not'


class Neg(UnaryExpr):
    """{{ -foo }}"""
    operator = '-'


class Pos(UnaryExpr):
    """{{ +foo }}"""
    operator = '+'