Add pylint to depot_tools.

third_party/logilab/astng/node_classes.py

Index: third_party/logilab/astng/node_classes.py
diff --git a/third_party/logilab/astng/node_classes.py b/third_party/logilab/astng/node_classes.py
new file mode 100644
index 0000000000000000000000000000000000000000..607ad9074f14183ab0072e8c860d04a38ddb8e2d
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+++ b/third_party/logilab/astng/node_classes.py
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+# copyright 2003-2011 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
+# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
+# copyright 2003-2010 Sylvain Thenault, all rights reserved.
+# contact mailto:thenault@gmail.com
+#
+# This file is part of logilab-astng.
+#
+# logilab-astng is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Lesser General Public License as published by the
+# Free Software Foundation, either version 2.1 of the License, or (at your
+# option) any later version.
+#
+# logilab-astng is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
+# for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License along
+# with logilab-astng. If not, see <http://www.gnu.org/licenses/>.
+"""Module for some node classes. More nodes in scoped_nodes.py
+"""
+
+import sys
+
+from logilab.astng import BUILTINS_MODULE
+from logilab.astng.exceptions import NoDefault
+from logilab.astng.bases import (NodeNG, Statement, Instance, InferenceContext,
+                                 _infer_stmts, YES)
+from logilab.astng.mixins import BlockRangeMixIn, AssignTypeMixin, \
+                                 ParentAssignTypeMixin, FromImportMixIn
+
+
+def unpack_infer(stmt, context=None):
+    """recursively generate nodes inferred by the given statement.
+    If the inferred value is a list or a tuple, recurse on the elements
+    """
+    if isinstance(stmt, (List, Tuple)):
+        for elt in stmt.elts:
+            for infered_elt in unpack_infer(elt, context):
+                yield infered_elt
+        return
+    infered = stmt.infer(context).next()
+    if infered is stmt or infered is YES:
+        yield infered
+        return
+    for infered in stmt.infer(context):
+        for inf_inf in unpack_infer(infered, context):
+            yield inf_inf
+
+
+def are_exclusive(stmt1, stmt2, exceptions=None):
+    """return true if the two given statements are mutually exclusive
+
+    `exceptions` may be a list of exception names. If specified, discard If
+    branches and check one of the statement is in an exception handler catching
+    one of the given exceptions.
+
+    algorithm :
+     1) index stmt1's parents
+     2) climb among stmt2's parents until we find a common parent
+     3) if the common parent is a If or TryExcept statement, look if nodes are
+        in exclusive branches
+    """
+    # index stmt1's parents
+    stmt1_parents = {}
+    children = {}
+    node = stmt1.parent
+    previous = stmt1
+    while node:
+        stmt1_parents[node] = 1
+        children[node] = previous
+        previous = node
+        node = node.parent
+    # climb among stmt2's parents until we find a common parent
+    node = stmt2.parent
+    previous = stmt2
+    while node:
+        if node in stmt1_parents:
+            # if the common parent is a If or TryExcept statement, look if
+            # nodes are in exclusive branches
+            if isinstance(node, If) and exceptions is None:
+                if (node.locate_child(previous)[1]
+                    is not node.locate_child(children[node])[1]):
+                    return True
+            elif isinstance(node, TryExcept):
+                c2attr, c2node = node.locate_child(previous)
+                c1attr, c1node = node.locate_child(children[node])
+                if c1node is not c2node:
+                    if ((c2attr == 'body' and c1attr == 'handlers' and children[node].catch(exceptions)) or
+                        (c2attr == 'handlers' and c1attr == 'body' and previous.catch(exceptions)) or
+                        (c2attr == 'handlers' and c1attr == 'orelse') or
+                        (c2attr == 'orelse' and c1attr == 'handlers')):
+                        return True
+                elif c2attr == 'handlers' and c1attr == 'handlers':
+                    return previous is not children[node]
+            return False
+        previous = node
+        node = node.parent
+    return False
+
+
+class LookupMixIn(object):
+    """Mixin looking up a name in the right scope
+    """
+
+    def lookup(self, name):
+        """lookup a variable name
+
+        return the scope node and the list of assignments associated to the given
+        name according to the scope where it has been found (locals, globals or
+        builtin)
+
+        The lookup is starting from self's scope. If self is not a frame itself and
+        the name is found in the inner frame locals, statements will be filtered
+        to remove ignorable statements according to self's location
+        """
+        return self.scope().scope_lookup(self, name)
+
+    def ilookup(self, name):
+        """infered lookup
+
+        return an iterator on infered values of the statements returned by
+        the lookup method
+        """
+        frame, stmts = self.lookup(name)
+        context = InferenceContext()
+        return _infer_stmts(stmts, context, frame)
+
+    def _filter_stmts(self, stmts, frame, offset):
+        """filter statements to remove ignorable statements.
+
+        If self is not a frame itself and the name is found in the inner
+        frame locals, statements will be filtered to remove ignorable
+        statements according to self's location
+        """
+        # if offset == -1, my actual frame is not the inner frame but its parent
+        #
+        # class A(B): pass
+        #
+        # we need this to resolve B correctly
+        if offset == -1:
+            myframe = self.frame().parent.frame()
+        else:
+            myframe = self.frame()
+        if not myframe is frame or self is frame:
+            return stmts
+        mystmt = self.statement()
+        # line filtering if we are in the same frame
+        #
+        # take care node may be missing lineno information (this is the case for
+        # nodes inserted for living objects)
+        if myframe is frame and mystmt.fromlineno is not None:
+            assert mystmt.fromlineno is not None, mystmt
+            mylineno = mystmt.fromlineno + offset
+        else:
+            # disabling lineno filtering
+            mylineno = 0
+        _stmts = []
+        _stmt_parents = []
+        for node in stmts:
+            stmt = node.statement()
+            # line filtering is on and we have reached our location, break
+            if mylineno > 0 and stmt.fromlineno > mylineno:
+                break
+            assert hasattr(node, 'ass_type'), (node, node.scope(),
+                                               node.scope().locals)
+            ass_type = node.ass_type()
+
+            if node.has_base(self):
+                break
+
+            _stmts, done = ass_type._get_filtered_stmts(self, node, _stmts, mystmt)
+            if done:
+                break
+
+            optional_assign = ass_type.optional_assign
+            if optional_assign and ass_type.parent_of(self):
+                # we are inside a loop, loop var assigment is hidding previous
+                # assigment
+                _stmts = [node]
+                _stmt_parents = [stmt.parent]
+                continue
+
+            # XXX comment various branches below!!!
+            try:
+                pindex = _stmt_parents.index(stmt.parent)
+            except ValueError:
+                pass
+            else:
+                # we got a parent index, this means the currently visited node
+                # is at the same block level as a previously visited node
+                if _stmts[pindex].ass_type().parent_of(ass_type):
+                    # both statements are not at the same block level
+                    continue
+                # if currently visited node is following previously considered
+                # assignement and both are not exclusive, we can drop the
+                # previous one. For instance in the following code ::
+                #
+                #   if a:
+                #     x = 1
+                #   else:
+                #     x = 2
+                #   print x
+                #
+                # we can't remove neither x = 1 nor x = 2 when looking for 'x'
+                # of 'print x'; while in the following ::
+                #
+                #   x = 1
+                #   x = 2
+                #   print x
+                #
+                # we can remove x = 1 when we see x = 2
+                #
+                # moreover, on loop assignment types, assignment won't
+                # necessarily be done if the loop has no iteration, so we don't
+                # want to clear previous assigments if any (hence the test on
+                # optional_assign)
+                if not (optional_assign or are_exclusive(_stmts[pindex], node)):
+                    del _stmt_parents[pindex]
+                    del _stmts[pindex]
+            if isinstance(node, AssName):
+                if not optional_assign and stmt.parent is mystmt.parent:
+                    _stmts = []
+                    _stmt_parents = []
+            elif isinstance(node, DelName):
+                _stmts = []
+                _stmt_parents = []
+                continue
+            if not are_exclusive(self, node):
+                _stmts.append(node)
+                _stmt_parents.append(stmt.parent)
+        return _stmts
+
+# Name classes
+
+class AssName(LookupMixIn, ParentAssignTypeMixin, NodeNG):
+    """class representing an AssName node"""
+
+
+class DelName(LookupMixIn, ParentAssignTypeMixin, NodeNG):
+    """class representing a DelName node"""
+
+
+class Name(LookupMixIn, NodeNG):
+    """class representing a Name node"""
+
+
+
+
+#####################   node classes   ########################################
+
+class Arguments(NodeNG, AssignTypeMixin):
+    """class representing an Arguments node"""
+    _astng_fields = ('args', 'defaults')
+    args = None
+    defaults = None
+
+    def __init__(self, vararg=None, kwarg=None):
+        self.vararg = vararg
+        self.kwarg = kwarg
+
+    def _infer_name(self, frame, name):
+        if self.parent is frame:
+            return name
+        return None
+
+    def format_args(self):
+        """return arguments formatted as string"""
+        result = [_format_args(self.args, self.defaults)]
+        if self.vararg:
+            result.append('*%s' % self.vararg)
+        if self.kwarg:
+            result.append('**%s' % self.kwarg)
+        return ', '.join(result)
+
+    def default_value(self, argname):
+        """return the default value for an argument
+
+        :raise `NoDefault`: if there is no default value defined
+        """
+        i = _find_arg(argname, self.args)[0]
+        if i is not None:
+            idx = i - (len(self.args) - len(self.defaults))
+            if idx >= 0:
+                return self.defaults[idx]
+        raise NoDefault()
+
+    def is_argument(self, name):
+        """return True if the name is defined in arguments"""
+        if name == self.vararg:
+            return True
+        if name == self.kwarg:
+            return True
+        return self.find_argname(name, True)[1] is not None
+
+    def find_argname(self, argname, rec=False):
+        """return index and Name node with given name"""
+        if self.args: # self.args may be None in some cases (builtin function)
+            return _find_arg(argname, self.args, rec)
+        return None, None
+
+
+def _find_arg(argname, args, rec=False):
+    for i, arg in enumerate(args):
+        if isinstance(arg, Tuple):
+            if rec:
+                found = _find_arg(argname, arg.elts)
+                if found[0] is not None:
+                    return found
+        elif arg.name == argname:
+            return i, arg
+    return None, None
+
+
+def _format_args(args, defaults=None):
+    values = []
+    if args is None:
+        return ''
+    if defaults is not None:
+        default_offset = len(args) - len(defaults)
+    for i, arg in enumerate(args):
+        if isinstance(arg, Tuple):
+            values.append('(%s)' % _format_args(arg.elts))
+        else:
+            values.append(arg.name)
+            if defaults is not None and i >= default_offset:
+                values[-1] += '=' + defaults[i-default_offset].as_string()
+    return ', '.join(values)
+
+
+class AssAttr(NodeNG, ParentAssignTypeMixin):
+    """class representing an AssAttr node"""
+    _astng_fields = ('expr',)
+    expr = None
+
+class Assert(Statement):
+    """class representing an Assert node"""
+    _astng_fields = ('test', 'fail',)
+    test = None
+    fail = None
+
+class Assign(Statement, AssignTypeMixin):
+    """class representing an Assign node"""
+    _astng_fields = ('targets', 'value',)
+    targets = None
+    value = None
+
+class AugAssign(Statement, AssignTypeMixin):
+    """class representing an AugAssign node"""
+    _astng_fields = ('target', 'value',)
+    target = None
+    value = None
+
+class Backquote(NodeNG):
+    """class representing a Backquote node"""
+    _astng_fields = ('value',)
+    value = None
+
+class BinOp(NodeNG):
+    """class representing a BinOp node"""
+    _astng_fields = ('left', 'right',)
+    left = None
+    right = None
+
+class BoolOp(NodeNG):
+    """class representing a BoolOp node"""
+    _astng_fields = ('values',)
+    values = None
+
+class Break(Statement):
+    """class representing a Break node"""
+
+
+class CallFunc(NodeNG):
+    """class representing a CallFunc node"""
+    _astng_fields = ('func', 'args', 'starargs', 'kwargs')
+    func = None
+    args = None
+    starargs = None
+    kwargs = None
+
+    def __init__(self):
+        self.starargs = None
+        self.kwargs = None
+
+class Compare(NodeNG):
+    """class representing a Compare node"""
+    _astng_fields = ('left', 'ops',)
+    left = None
+    ops = None
+
+    def get_children(self):
+        """override get_children for tuple fields"""
+        yield self.left
+        for _, comparator in self.ops:
+            yield comparator # we don't want the 'op'
+
+    def last_child(self):
+        """override last_child"""
+        # XXX maybe if self.ops:
+        return self.ops[-1][1]
+        #return self.left
+
+class Comprehension(NodeNG):
+    """class representing a Comprehension node"""
+    _astng_fields = ('target', 'iter' ,'ifs')
+    target = None
+    iter = None
+    ifs = None
+
+    optional_assign = True
+    def ass_type(self):
+        return self
+
+    def _get_filtered_stmts(self, lookup_node, node, stmts, mystmt):
+        """method used in filter_stmts"""
+        if self is mystmt:
+            if isinstance(lookup_node, (Const, Name)):
+                return [lookup_node], True
+
+        elif self.statement() is mystmt:
+            # original node's statement is the assignment, only keeps
+            # current node (gen exp, list comp)
+
+            return [node], True
+
+        return stmts, False
+
+
+class Const(NodeNG, Instance):
+    """represent a constant node like num, str, bool, None, bytes"""
+
+    def __init__(self, value=None):
+        self.value = value
+
+    def getitem(self, index, context=None):
+        if isinstance(self.value, basestring):
+            return Const(self.value[index])
+        raise TypeError('%r (value=%s)' % (self, self.value))
+
+    def has_dynamic_getattr(self):
+        return False
+
+    def itered(self):
+        if isinstance(self.value, basestring):
+            return self.value
+        raise TypeError()
+
+    def pytype(self):
+        return self._proxied.qname()
+
+
+class Continue(Statement):
+    """class representing a Continue node"""
+
+
+class Decorators(NodeNG):
+    """class representing a Decorators node"""
+    _astng_fields = ('nodes',)
+    nodes = None
+
+    def __init__(self, nodes=None):
+        self.nodes = nodes
+
+    def scope(self):
+        # skip the function node to go directly to the upper level scope
+        return self.parent.parent.scope()
+
+class DelAttr(NodeNG, ParentAssignTypeMixin):
+    """class representing a DelAttr node"""
+    _astng_fields = ('expr',)
+    expr = None
+
+
+class Delete(Statement, AssignTypeMixin):
+    """class representing a Delete node"""
+    _astng_fields = ('targets',)
+    targets = None
+
+
+class Dict(NodeNG, Instance):
+    """class representing a Dict node"""
+    _astng_fields = ('items',)
+
+    def __init__(self, items=None):
+        if items is None:
+            self.items = []
+        else:
+            self.items = [(const_factory(k), const_factory(v))
+                          for k,v in items.iteritems()]
+
+    def pytype(self):
+        return '%s.dict' % BUILTINS_MODULE
+
+    def get_children(self):
+        """get children of a Dict node"""
+        # overrides get_children
+        for key, value in self.items:
+            yield key
+            yield value
+
+    def last_child(self):
+        """override last_child"""
+        if self.items:
+            return self.items[-1][1]
+        return None
+
+    def itered(self):
+        return self.items[::2]
+
+    def getitem(self, key, context=None):
+        for i in xrange(0, len(self.items), 2):
+            for inferedkey in self.items[i].infer(context):
+                if inferedkey is YES:
+                    continue
+                if isinstance(inferedkey, Const) and inferedkey.value == key:
+                    return self.items[i+1]
+        raise IndexError(key)
+
+
+class Discard(Statement):
+    """class representing a Discard node"""
+    _astng_fields = ('value',)
+    value = None
+
+
+class Ellipsis(NodeNG):
+    """class representing an Ellipsis node"""
+
+
+class EmptyNode(NodeNG):
+    """class representing an EmptyNode node"""
+
+
+class ExceptHandler(Statement, AssignTypeMixin):
+    """class representing an ExceptHandler node"""
+    _astng_fields = ('type', 'name', 'body',)
+    type = None
+    name = None
+    body = None
+
+    def _blockstart_toline(self):
+        if self.name:
+            return self.name.tolineno
+        elif self.type:
+            return self.type.tolineno
+        else:
+            return self.lineno
+
+    def set_line_info(self, lastchild):
+        self.fromlineno = self.lineno
+        self.tolineno = lastchild.tolineno
+        self.blockstart_tolineno = self._blockstart_toline()
+
+    def catch(self, exceptions):
+        if self.type is None or exceptions is None:
+            return True
+        for node in self.type.nodes_of_class(Name):
+            if node.name in exceptions:
+                return True
+
+
+class Exec(Statement):
+    """class representing an Exec node"""
+    _astng_fields = ('expr', 'globals', 'locals',)
+    expr = None
+    globals = None
+    locals = None
+
+
+class ExtSlice(NodeNG):
+    """class representing an ExtSlice node"""
+    _astng_fields = ('dims',)
+    dims = None
+
+class For(BlockRangeMixIn, AssignTypeMixin, Statement):
+    """class representing a For node"""
+    _astng_fields = ('target', 'iter', 'body', 'orelse',)
+    target = None
+    iter = None
+    body = None
+    orelse = None
+
+    optional_assign = True
+    def _blockstart_toline(self):
+        return self.iter.tolineno
+
+
+class From(FromImportMixIn, Statement):
+    """class representing a From node"""
+
+    def __init__(self,  fromname, names, level=0):
+        self.modname = fromname
+        self.names = names
+        self.level = level
+
+class Getattr(NodeNG):
+    """class representing a Getattr node"""
+    _astng_fields = ('expr',)
+    expr = None
+
+
+class Global(Statement):
+    """class representing a Global node"""
+
+    def __init__(self, names):
+        self.names = names
+
+    def _infer_name(self, frame, name):
+        return name
+
+
+class If(BlockRangeMixIn, Statement):
+    """class representing an If node"""
+    _astng_fields = ('test', 'body', 'orelse')
+    test = None
+    body = None
+    orelse = None
+
+    def _blockstart_toline(self):
+        return self.test.tolineno
+
+    def block_range(self, lineno):
+        """handle block line numbers range for if statements"""
+        if lineno == self.body[0].fromlineno:
+            return lineno, lineno
+        if lineno <= self.body[-1].tolineno:
+            return lineno, self.body[-1].tolineno
+        return self._elsed_block_range(lineno, self.orelse,
+                                       self.body[0].fromlineno - 1)
+
+
+class IfExp(NodeNG):
+    """class representing an IfExp node"""
+    _astng_fields = ('test', 'body', 'orelse')
+    test = None
+    body = None
+    orelse = None
+
+
+class Import(FromImportMixIn, Statement):
+    """class representing an Import node"""
+
+
+class Index(NodeNG):
+    """class representing an Index node"""
+    _astng_fields = ('value',)
+    value = None
+
+
+class Keyword(NodeNG):
+    """class representing a Keyword node"""
+    _astng_fields = ('value',)
+    value = None
+
+
+class List(NodeNG, Instance, ParentAssignTypeMixin):
+    """class representing a List node"""
+    _astng_fields = ('elts',)
+
+    def __init__(self, elts=None):
+        if elts is None:
+            self.elts = []
+        else:
+            self.elts = [const_factory(e) for e in elts]
+
+    def pytype(self):
+        return '%s.list' % BUILTINS_MODULE
+
+    def getitem(self, index, context=None):
+        return self.elts[index]
+
+    def itered(self):
+        return self.elts
+
+
+class Nonlocal(Statement):
+    """class representing a Nonlocal node"""
+
+    def __init__(self, names):
+        self.names = names
+
+    def _infer_name(self, frame, name):
+        return name
+
+
+class Pass(Statement):
+    """class representing a Pass node"""
+
+
+class Print(Statement):
+    """class representing a Print node"""
+    _astng_fields = ('dest', 'values',)
+    dest = None
+    values = None
+
+
+class Raise(Statement):
+    """class representing a Raise node"""
+    exc = None
+    if sys.version_info < (3, 0):
+        _astng_fields = ('exc', 'inst', 'tback')
+        inst = None
+        tback = None
+    else:
+        _astng_fields = ('exc', 'cause')
+        exc = None
+        cause = None
+
+    def raises_not_implemented(self):
+        if not self.exc:
+            return
+        for name in self.exc.nodes_of_class(Name):
+            if name.name == 'NotImplementedError':
+                return True
+
+
+class Return(Statement):
+    """class representing a Return node"""
+    _astng_fields = ('value',)
+    value = None
+
+
+class Set(NodeNG, Instance, ParentAssignTypeMixin):
+    """class representing a Set node"""
+    _astng_fields = ('elts',)
+
+    def __init__(self, elts=None):
+        if elts is None:
+            self.elts = []
+        else:
+            self.elts = [const_factory(e) for e in elts]
+
+    def pytype(self):
+        return '%s.set' % BUILTINS_MODULE
+
+    def itered(self):
+        return self.elts
+
+
+class Slice(NodeNG):
+    """class representing a Slice node"""
+    _astng_fields = ('lower', 'upper', 'step')
+    lower = None
+    upper = None
+    step = None
+
+class Starred(NodeNG):
+    """class representing a Starred node"""
+    _astng_fields = ('value',)
+    value = None
+
+
+class Subscript(NodeNG):
+    """class representing a Subscript node"""
+    _astng_fields = ('value', 'slice')
+    value = None
+    slice = None
+
+
+class TryExcept(BlockRangeMixIn, Statement):
+    """class representing a TryExcept node"""
+    _astng_fields = ('body', 'handlers', 'orelse',)
+    body = None
+    handlers = None
+    orelse = None
+
+    def _infer_name(self, frame, name):
+        return name
+
+    def _blockstart_toline(self):
+        return self.lineno
+
+    def block_range(self, lineno):
+        """handle block line numbers range for try/except statements"""
+        last = None
+        for exhandler in self.handlers:
+            if exhandler.type and lineno == exhandler.type.fromlineno:
+                return lineno, lineno
+            if exhandler.body[0].fromlineno <= lineno <= exhandler.body[-1].tolineno:
+                return lineno, exhandler.body[-1].tolineno
+            if last is None:
+                last = exhandler.body[0].fromlineno - 1
+        return self._elsed_block_range(lineno, self.orelse, last)
+
+
+class TryFinally(BlockRangeMixIn, Statement):
+    """class representing a TryFinally node"""
+    _astng_fields = ('body', 'finalbody',)
+    body = None
+    finalbody = None
+
+    def _blockstart_toline(self):
+        return self.lineno
+
+    def block_range(self, lineno):
+        """handle block line numbers range for try/finally statements"""
+        child = self.body[0]
+        # py2.5 try: except: finally:
+        if (isinstance(child, TryExcept) and child.fromlineno == self.fromlineno
+            and lineno > self.fromlineno and lineno <= child.tolineno):
+            return child.block_range(lineno)
+        return self._elsed_block_range(lineno, self.finalbody)
+
+
+class Tuple(NodeNG, Instance, ParentAssignTypeMixin):
+    """class representing a Tuple node"""
+    _astng_fields = ('elts',)
+
+    def __init__(self, elts=None):
+        if elts is None:
+            self.elts = []
+        else:
+            self.elts = [const_factory(e) for e in elts]
+
+    def pytype(self):
+        return '%s.tuple' % BUILTINS_MODULE
+
+    def getitem(self, index, context=None):
+        return self.elts[index]
+
+    def itered(self):
+        return self.elts
+
+
+class UnaryOp(NodeNG):
+    """class representing an UnaryOp node"""
+    _astng_fields = ('operand',)
+    operand = None
+
+
+class While(BlockRangeMixIn, Statement):
+    """class representing a While node"""
+    _astng_fields = ('test', 'body', 'orelse',)
+    test = None
+    body = None
+    orelse = None
+
+    def _blockstart_toline(self):
+        return self.test.tolineno
+
+    def block_range(self, lineno):
+        """handle block line numbers range for for and while statements"""
+        return self. _elsed_block_range(lineno, self.orelse)
+
+
+class With(BlockRangeMixIn, AssignTypeMixin, Statement):
+    """class representing a With node"""
+    _astng_fields = ('expr', 'vars', 'body')
+    expr = None
+    vars = None
+    body = None
+
+    def _blockstart_toline(self):
+        if self.vars:
+            return self.vars.tolineno
+        else:
+            return self.expr.tolineno
+
+
+class Yield(NodeNG):
+    """class representing a Yield node"""
+    _astng_fields = ('value',)
+    value = None
+
+# constants ##############################################################
+
+CONST_CLS = {
+    list: List,
+    tuple: Tuple,
+    dict: Dict,
+    set: Set,
+    type(None): Const,
+    }
+
+def _update_const_classes():
+    """update constant classes, so the keys of CONST_CLS can be reused"""
+    klasses = (bool, int, float, complex, str)
+    if sys.version_info < (3, 0):
+        klasses += (unicode, long)
+    if sys.version_info >= (2, 6):
+        klasses += (bytes,)
+    for kls in klasses:
+        CONST_CLS[kls] = Const
+_update_const_classes()
+
+def const_factory(value):
+    """return an astng node for a python value"""
+    # since const_factory is called to evaluate content of container (eg list,
+    # tuple), it may be called with some node as argument that should be left
+    # untouched
+    if isinstance(value, NodeNG):
+        return value
+    try:
+        return CONST_CLS[value.__class__](value)
+    except (KeyError, AttributeError):
+        # some constants (like from gtk._gtk) don't have their class in
+        # CONST_CLS, though we can "assert isinstance(value, tuple(CONST_CLS))"
+        if isinstance(value, tuple(CONST_CLS)):
+            return Const(value)
+        node = EmptyNode()
+        node.object = value
+        return node