Move YES to astroid.util.

YES is needed by other components of astroid, components which aren't
necessarily related to astroid.bases. In order to reduce circular
interdependencies between components, YES is moved into a new module,
tailored for various *utilities*.

19 files changed, 233 insertions, 195 deletions

diff --git a/astroid/__init__.py b/astroid/__init__.py
index c00c678..aecee7f 100644
--- a/astroid/__init__.py
+++ b/astroid/__init__.py
@@ -60,10 +60,11 @@ from astroid import inference
 
 # more stuff available
 from astroid import raw_building
-from astroid.bases import YES, Instance, BoundMethod, UnboundMethod
+from astroid.bases import Instance, BoundMethod, UnboundMethod
 from astroid.node_classes import are_exclusive, unpack_infer
 from astroid.scoped_nodes import builtin_lookup
 from astroid.builder import parse
+from astroid.util import YES
 
 # make a manager instance (borg) accessible from astroid package
 from astroid.manager import AstroidManager
diff --git a/astroid/bases.py b/astroid/bases.py
index fc17fd5..e30ae15 100644
--- a/astroid/bases.py
+++ b/astroid/bases.py
@@ -25,6 +25,7 @@ from contextlib import contextmanager
 from astroid.exceptions import (InferenceError, AstroidError, NotFoundError,
                                 UnresolvableName, UseInferenceDefault)
 from astroid.decorators import cachedproperty
+from astroid import util
 
 
 if sys.version_info >= (3, 0):
@@ -53,7 +54,7 @@ def _is_property(meth):
     if PROPERTIES.intersection(meth.decoratornames()):
         return True
     stripped = {name.split(".")[-1] for name in meth.decoratornames()
-                if name is not YES}
+                if name is not util.YES}
     return any(name in stripped for name in POSSIBLE_PROPERTIES)
 
 
@@ -134,7 +135,7 @@ def _infer_stmts(stmts, context, frame=None):
         context = InferenceContext()
 
     for stmt in stmts:
-        if stmt is YES:
+        if stmt is util.YES:
             yield stmt
             infered = True
             continue
@@ -146,43 +147,24 @@ def _infer_stmts(stmts, context, frame=None):
         except UnresolvableName:
             continue
         except InferenceError:
-            yield YES
+            yield util.YES
             infered = True
     if not infered:
         raise InferenceError(str(stmt))
 
 
-class _Yes(object):
-    """Special inference object, which is returned when inference fails."""
-    def __repr__(self):
-        return 'YES'
-
-    def __getattribute__(self, name):
-        if name == 'next':
-            raise AttributeError('next method should not be called')
-        if name.startswith('__') and name.endswith('__'):
-            return super(_Yes, self).__getattribute__(name)
-        return self
-
-    def __call__(self, *args, **kwargs):
-        return self
-
-
-YES = _Yes()
-
-
 def _infer_method_result_truth(instance, method_name, context):
     # Get the method from the instance and try to infer
     # its return's truth value.
     meth = next(instance.igetattr(method_name, context=context), None)
     if meth and hasattr(meth, 'infer_call_result'):
         for value in meth.infer_call_result(instance, context=context):
-            if value is YES:
+            if value is util.YES:
                 return value
 
             inferred = next(value.infer(context=context))
             return inferred.bool_value()
-    return YES
+    return util.YES
 
 
 class Instance(Proxy):
@@ -262,7 +244,7 @@ class Instance(Proxy):
         """infer what a class instance is returning when called"""
         infered = False
         for node in self._proxied.igetattr('__call__', context):
-            if node is YES:
+            if node is util.YES:
                 continue
             for res in node.infer_call_result(caller, context):
                 infered = True
@@ -350,7 +332,7 @@ class UnboundMethod(Proxy):
         if (self._proxied.name == '__new__' and
                 self._proxied.parent.frame().qname() == '%s.object' % BUILTINS):
             infer = caller.args[0].infer() if caller.args else []
-            return ((x is YES and x or Instance(x)) for x in infer)
+            return ((x is util.YES and x or Instance(x)) for x in infer)
         return self._proxied.infer_call_result(caller, context)
 
     def bool_value(self):
@@ -427,7 +409,7 @@ def yes_if_nothing_infered(func):
             infered = True
             yield node
         if not infered:
-            yield YES
+            yield util.YES
     return wrapper
 
 def raise_if_nothing_infered(func):
@@ -730,7 +712,7 @@ class NodeNG(object):
             * YES: the inference engine is uncertain of the
               node's value.
         """
-        return YES
+        return util.YES
 
 
 class Statement(NodeNG):
diff --git a/astroid/brain/builtin_inference.py b/astroid/brain/builtin_inference.py
index 451d662..0fede7e 100644
--- a/astroid/brain/builtin_inference.py
+++ b/astroid/brain/builtin_inference.py
@@ -6,12 +6,13 @@ from textwrap import dedent
 
 import six
 from astroid import (MANAGER, UseInferenceDefault, NotFoundError,
-                     inference_tip, YES, InferenceError, UnresolvableName)
+                     inference_tip, InferenceError, UnresolvableName)
 from astroid.builder import AstroidBuilder
 from astroid import helpers
 from astroid import nodes
 from astroid import objects
 from astroid import scoped_nodes
+from astroid import util
 
 
 def _extend_str(class_node, rvalue):
@@ -119,10 +120,10 @@ def _generic_inference(node, context, node_type, transform):
             infered = next(arg.infer(context=context))
         except (InferenceError, StopIteration):
             raise UseInferenceDefault()
-        if infered is YES:
+        if infered is util.YES:
             raise UseInferenceDefault()
         transformed = transform(infered)
-    if not transformed or transformed is YES:
+    if not transformed or transformed is util.YES:
         raise UseInferenceDefault()
     return transformed
 
@@ -295,7 +296,7 @@ def infer_super(node, context=None):
         except InferenceError:
             raise UseInferenceDefault
 
-    if mro_pointer is YES or mro_type is YES:
+    if mro_pointer is util.YES or mro_type is util.YES:
         # No way we could understand this.
         raise UseInferenceDefault
 
@@ -319,11 +320,11 @@ def _infer_getattr_args(node, context):
     except InferenceError:
         raise UseInferenceDefault
 
-    if obj is YES or attr is YES:
+    if obj is util.YES or attr is util.YES:
         # If one of the arguments is something we can't infer,
         # then also make the result of the getattr call something
         # which is unknown.
-        return YES, YES
+        return util.YES, util.YES
 
     is_string = (isinstance(attr, nodes.Const) and
                  isinstance(attr.value, six.string_types))
@@ -341,8 +342,8 @@ def infer_getattr(node, context=None):
     lookup will be done.
     """
     obj, attr = _infer_getattr_args(node, context)
-    if obj is YES or attr is YES:
-        return YES
+    if obj is util.YES or attr is util.YES:
+        return util.YES
 
     try:
         return next(obj.igetattr(attr, context=context))
@@ -368,12 +369,12 @@ def infer_hasattr(node, context=None):
     """
     try:
         obj, attr = _infer_getattr_args(node, context)
-        if obj is YES or attr is YES:
-            return YES
+        if obj is util.YES or attr is util.YES:
+            return util.YES
         obj.getattr(attr, context=context)
     except UseInferenceDefault:
         # Can't infer something from this function call.
-        return YES
+        return util.YES
     except NotFoundError:
         # Doesn't have it.
         return nodes.Const(False)
@@ -396,9 +397,9 @@ def infer_callable(node, context=None):
     try:
         inferred = next(argument.infer(context=context))
     except InferenceError:
-        return YES
-    if inferred is YES:
-        return YES
+        return util.YES
+    if inferred is util.YES:
+        return util.YES
     return nodes.Const(inferred.callable())
 
 
@@ -415,13 +416,13 @@ def infer_bool(node, context=None):
     try:
         inferred = next(argument.infer(context=context))
     except InferenceError:
-        return YES
-    if inferred is YES:
-        return YES
+        return util.YES
+    if inferred is util.YES:
+        return util.YES
 
     bool_value = inferred.bool_value()
-    if bool_value is YES:
-        return YES
+    if bool_value is util.YES:
+        return util.YES
     return nodes.Const(bool_value)
 
 
diff --git a/astroid/brain/py2stdlib.py b/astroid/brain/py2stdlib.py
index 206bd8c..a7e013a 100644
--- a/astroid/brain/py2stdlib.py
+++ b/astroid/brain/py2stdlib.py
@@ -12,10 +12,11 @@ from textwrap import dedent
 from astroid import (
     MANAGER, AsStringRegexpPredicate,
     UseInferenceDefault, inference_tip, BoundMethod,
-    YES, InferenceError, register_module_extender)
+    InferenceError, register_module_extender)
 from astroid import exceptions
 from astroid import nodes
 from astroid.builder import AstroidBuilder
+from astroid import util
 
 PY3K = sys.version_info > (3, 0)
 PY33 = sys.version_info >= (3, 3)
@@ -28,7 +29,7 @@ def infer_func_form(node, base_type, context=None, enum=False):
     def infer_first(node):
         try:
             value = next(node.infer(context=context))
-            if value is YES:
+            if value is util.YES:
                 raise UseInferenceDefault()
             else:
                 return value
diff --git a/astroid/builder.py b/astroid/builder.py
index 2824647..5d907c8 100644
--- a/astroid/builder.py
+++ b/astroid/builder.py
@@ -33,6 +33,7 @@ from astroid import manager
 from astroid import modutils
 from astroid import raw_building
 from astroid import rebuilder
+from astroid import util
 
 
 def _parse(string):
@@ -216,7 +217,7 @@ class AstroidBuilder(raw_building.InspectBuilder):
         try:
             frame = node.frame()
             for infered in node.expr.infer():
-                if infered is bases.YES:
+                if infered is util.YES:
                     continue
                 try:
                     if infered.__class__ is bases.Instance:
diff --git a/astroid/helpers.py b/astroid/helpers.py
index 1148ada..21dd76c 100644
--- a/astroid/helpers.py
+++ b/astroid/helpers.py
@@ -27,6 +27,7 @@ from astroid import exceptions
 from astroid import manager

 from astroid import raw_building

 from astroid import scoped_nodes

+from astroid import util

 

 

 BUILTINS = six.moves.builtins.__name__

@@ -89,9 +90,9 @@ def object_type(node, context=None):
     try:

         types = set(_object_type(node, context))

     except exceptions.InferenceError:

-        return bases.YES

+        return util.YES

     if len(types) > 1 or not types:

-        return bases.YES

+        return util.YES

     return list(types)[0]

 

 

@@ -135,7 +136,7 @@ def has_known_bases(klass, context=None):
 

 def _type_check(type1, type2):

     if not all(map(has_known_bases, (type1, type2))):

-        return bases.YES

+        return util.YES

 

     if not all([type1.newstyle, type2.newstyle]):

         return False

@@ -143,7 +144,7 @@ def _type_check(type1, type2):
         return type1 in type2.mro()[:-1]

     except exceptions.MroError:

         # The MRO is invalid.

-        return bases.YES

+        return util.YES

 

 

 def is_subtype(type1, type2):

diff --git a/astroid/inference.py b/astroid/inference.py
index f05b163..ae8a5d2 100644
--- a/astroid/inference.py
+++ b/astroid/inference.py
@@ -25,6 +25,7 @@ import operator
 from astroid import helpers
 from astroid import nodes
 from astroid import protocols
+from astroid import util
 from astroid.manager import AstroidManager
 from astroid.exceptions import (
     AstroidError, InferenceError, NoDefault,
@@ -32,7 +33,7 @@ from astroid.exceptions import (
     UnaryOperationError,
     BinaryOperationError,
 )
-from astroid.bases import (YES, Instance, InferenceContext, BoundMethod,
+from astroid.bases import (Instance, InferenceContext, BoundMethod,
                            _infer_stmts, copy_context, path_wrapper,
                            raise_if_nothing_infered, yes_if_nothing_infered)
 
@@ -88,13 +89,13 @@ class CallContext(object):
                 if self.starargs is not None:
                     its = []
                     for infered in self.starargs.infer(context):
-                        if infered is YES:
-                            its.append((YES,))
+                        if infered is util.YES:
+                            its.append((util.YES,))
                             continue
                         try:
                             its.append(infered.getitem(argindex, context).infer(context))
                         except (InferenceError, AttributeError):
-                            its.append((YES,))
+                            its.append((util.YES,))
                         except (IndexError, TypeError):
                             continue
                     if its:
@@ -103,13 +104,13 @@ class CallContext(object):
         if self.kwargs is not None:
             its = []
             for infered in self.kwargs.infer(context=context):
-                if infered is YES:
-                    its.append((YES,))
+                if infered is util.YES:
+                    its.append((util.YES,))
                     continue
                 try:
                     its.append(infered.getitem(name, context).infer(context=context))
                 except (InferenceError, AttributeError):
-                    its.append((YES,))
+                    its.append((util.YES,))
                 except (IndexError, TypeError):
                     continue
             if its:
@@ -190,7 +191,7 @@ def infer_callfunc(self, context=None):
                                           kwargs=self.kwargs)
     callcontext.boundnode = None
     for callee in self.func.infer(context):
-        if callee is YES:
+        if callee is util.YES:
             yield callee
             continue
         try:
@@ -241,7 +242,7 @@ nodes.From._infer = path_wrapper(infer_from)
 def infer_getattr(self, context=None):
     """infer a Getattr node by using getattr on the associated object"""
     for owner in self.expr.infer(context):
-        if owner is YES:
+        if owner is util.YES:
             yield owner
             continue
         try:
@@ -271,13 +272,13 @@ nodes.Global._infer = path_wrapper(infer_global)
 def infer_subscript(self, context=None):
     """infer simple subscription such as [1,2,3][0] or (1,2,3)[-1]"""
     value = next(self.value.infer(context))
-    if value is YES:
-        yield YES
+    if value is util.YES:
+        yield util.YES
         return
 
     index = next(self.slice.infer(context))
-    if index is YES:
-        yield YES
+    if index is util.YES:
+        yield util.YES
         return
 
     if isinstance(index, nodes.Const):
@@ -286,13 +287,13 @@ def infer_subscript(self, context=None):
         except AttributeError:
             raise InferenceError()
         except (IndexError, TypeError):
-            yield YES
+            yield util.YES
             return
 
         # Prevent inferring if the infered subscript
         # is the same as the original subscripted object.
-        if self is assigned or assigned is YES:
-            yield YES
+        if self is assigned or assigned is util.YES:
+            yield util.YES
             return
         for infered in assigned.infer(context):
             yield infered
@@ -320,19 +321,19 @@ def _infer_boolop(self, context=None):
     try:
         values = [value.infer(context=context) for value in values]
     except InferenceError:
-        yield YES
+        yield util.YES
         return
 
     for pair in itertools.product(*values):
-        if any(item is YES for item in pair):
+        if any(item is util.YES for item in pair):
             # Can't infer the final result, just yield YES.
-            yield YES
+            yield util.YES
             continue
 
         bool_values = [item.bool_value() for item in pair]
-        if any(item is YES for item in bool_values):
+        if any(item is util.YES for item in bool_values):
             # Can't infer the final result, just yield YES.
-            yield YES
+            yield util.YES
             continue
 
         # Since the boolean operations are short circuited operations,
@@ -344,7 +345,7 @@ def _infer_boolop(self, context=None):
         #   0 and 1 -> 0
         #   1 or 0 -> 1
         #   0 or 1 -> 1
-        value = YES
+        value = util.YES
         for value, bool_value in zip(pair, bool_values):
             if predicate(bool_value):
                 yield value
@@ -363,7 +364,7 @@ def _filter_operation_errors(self, infer_callable, context, error):
             # For the sake of .infer(), we don't care about operation
             # errors, which is the job of pylint. So return something
             # which shows that we can't infer the result.
-            yield YES
+            yield util.YES
         else:
             yield result
 
@@ -383,10 +384,10 @@ def _infer_unaryop(self, context=None):
                 # value and negate its result, unless it is
                 # YES, which will be returned as is.
                 bool_value = operand.bool_value()
-                if bool_value is not YES:
+                if bool_value is not util.YES:
                     yield nodes.const_factory(not bool_value)
                 else:
-                    yield YES
+                    yield util.YES
             else:
                 if not isinstance(operand, Instance):
                     # The operation was used on something which
@@ -408,7 +409,7 @@ def _infer_unaryop(self, context=None):
                     # The unary operation special method was not found.
                     yield UnaryOperationError(operand, self.op, exc)
                 except InferenceError:
-                    yield YES
+                    yield util.YES
 
 
 @path_wrapper
@@ -561,11 +562,11 @@ def _infer_binary_operation(left, right, op, context, flow_factory):
         except NotFoundError:
             continue
         except InferenceError:
-            yield YES
+            yield util.YES
             return
         else:
-            if any(result is YES for result in results):
-                yield YES
+            if any(result is util.YES for result in results):
+                yield util.YES
                 return
 
             # TODO(cpopa): since the inferrence engine might return
@@ -577,7 +578,7 @@ def _infer_binary_operation(left, right, op, context, flow_factory):
                                   if _is_not_implemented(result))
             if not_implemented and not_implemented != len(results):
                 # Can't decide yet what this is, not yet though.
-                yield YES
+                yield util.YES
                 return
 
             for result in results:
@@ -597,9 +598,9 @@ def _infer_binop(self, context):
     op = self.op
 
     for lhs in left.infer(context=context):
-        if lhs is YES:
+        if lhs is util.YES:
             # Don't know how to process this.
-            yield YES
+            yield util.YES
             return
 
         # TODO(cpopa): if we have A() * A(), trying to infer
@@ -609,9 +610,9 @@ def _infer_binop(self, context):
         rhs_context = context.clone()
         rhs_context.path = set()
         for rhs in right.infer(context=rhs_context):
-            if rhs is YES:
+            if rhs is util.YES:
                 # Don't know how to process this.
-                yield YES
+                yield util.YES
                 return
 
             results = _infer_binary_operation(lhs, rhs, op,
@@ -636,9 +637,9 @@ def _infer_augassign(self, context=None):
     op = self.op
 
     for lhs in self.target.infer_lhs(context=context):
-        if lhs is YES:
+        if lhs is util.YES:
             # Don't know how to process this.
-            yield YES
+            yield util.YES
             return
 
         # TODO(cpopa): if we have A() * A(), trying to infer
@@ -648,9 +649,9 @@ def _infer_augassign(self, context=None):
         rhs_context = context.clone()
         rhs_context.path = set()
         for rhs in self.value.infer(context=rhs_context):
-            if rhs is YES:
+            if rhs is util.YES:
                 # Don't know how to process this.
-                yield YES
+                yield util.YES
                 return
 
             results = _infer_binary_operation(lhs, rhs, op,
@@ -696,14 +697,14 @@ nodes.AssAttr._infer = path_wrapper(infer_ass)
 
 def infer_empty_node(self, context=None):
     if not self.has_underlying_object():
-        yield YES
+        yield util.YES
     else:
         try:
             for infered in MANAGER.infer_ast_from_something(self.object,
                                                             context=context):
                 yield infered
         except AstroidError:
-            yield YES
+            yield util.YES
 nodes.EmptyNode._infer = path_wrapper(infer_empty_node)
 
 
diff --git a/astroid/node_classes.py b/astroid/node_classes.py
index 5f107ba..3b085df 100644
--- a/astroid/node_classes.py
+++ b/astroid/node_classes.py
@@ -25,10 +25,11 @@ from astroid.exceptions import (
     InferenceError, BinaryOperationError
 )
 from astroid.bases import (NodeNG, Statement, Instance, InferenceContext,
-                           _infer_stmts, YES, BUILTINS)
+                           _infer_stmts, BUILTINS)
 from astroid.mixins import (BlockRangeMixIn, AssignTypeMixin,
                             ParentAssignTypeMixin, FromImportMixIn)
 from astroid.decorators import cachedproperty
+from astroid import util
 
 
 def unpack_infer(stmt, context=None):
@@ -47,7 +48,7 @@ def unpack_infer(stmt, context=None):
         return
     # else, infer recursivly, except YES object that should be returned as is
     for infered in stmt.infer(context):
-        if infered is YES:
+        if infered is util.YES:
             yield infered
         else:
             for inf_inf in unpack_infer(infered, context):
@@ -623,7 +624,7 @@ class Dict(NodeNG, Instance):
     def getitem(self, lookup_key, context=None):
         for key, value in self.items:
             for inferedkey in key.infer(context):
-                if inferedkey is YES:
+                if inferedkey is util.YES:
                     continue
                 if isinstance(inferedkey, Const) \
                         and inferedkey.value == lookup_key:
diff --git a/astroid/protocols.py b/astroid/protocols.py
index 46a03be..9cbb555 100644
--- a/astroid/protocols.py
+++ b/astroid/protocols.py
@@ -30,11 +30,12 @@ from astroid.node_classes import unpack_infer
 from astroid.bases import (
     InferenceContext, copy_context,
     raise_if_nothing_infered, yes_if_nothing_infered,
-    Instance, YES, BoundMethod,
+    Instance, BoundMethod,
     Generator,
 )
 from astroid.nodes import const_factory
 from astroid import nodes
+from astroid import util
 
 
 def _reflected_name(name):
@@ -126,12 +127,12 @@ def const_infer_binary_op(self, operator, other, context, _):
                 # ArithmeticError is not enough: float >> float is a TypeError
                 yield not_implemented
             except Exception: # pylint: disable=broad-except
-                yield YES
+                yield util.YES
         except TypeError:
             yield not_implemented
     elif isinstance(self.value, six.string_types) and operator == '%':
         # TODO(cpopa): implement string interpolation later on.
-        yield YES
+        yield util.YES
     else:
         yield not_implemented
 
@@ -141,7 +142,7 @@ nodes.Const.infer_binary_op = yes_if_nothing_infered(const_infer_binary_op)
 def _multiply_seq_by_int(self, other, context):
     node = self.__class__()
     elts = [n for elt in self.elts for n in elt.infer(context)
-            if not n is YES] * other.value
+            if not n is util.YES] * other.value
     node.elts = elts
     return node
 
@@ -151,9 +152,9 @@ def tl_infer_binary_op(self, operator, other, context, method):
     if isinstance(other, self.__class__) and operator == '+':
         node = self.__class__()
         elts = [n for elt in self.elts for n in elt.infer(context)
-                if not n is YES]
+                if not n is util.YES]
         elts += [n for elt in other.elts for n in elt.infer(context)
-                 if not n is YES]
+                 if not n is util.YES]
         node.elts = elts
         yield node
     elif isinstance(other, nodes.Const) and operator == '*':
@@ -165,7 +166,7 @@ def tl_infer_binary_op(self, operator, other, context, method):
         # Verify if the instance supports __index__.
         as_index = class_as_index(other, context)
         if not as_index:
-            yield YES
+            yield util.YES
         else:
             yield _multiply_seq_by_int(self, as_index, context)
     else:
@@ -199,7 +200,7 @@ def _resolve_looppart(parts, asspath, context):
     asspath = asspath[:]
     index = asspath.pop(0)
     for part in parts:
-        if part is YES:
+        if part is util.YES:
             continue
         # XXX handle __iter__ and log potentially detected errors
         if not hasattr(part, 'itered'):
@@ -219,7 +220,7 @@ def _resolve_looppart(parts, asspath, context):
                 # we achieved to resolved the assignment path,
                 # don't infer the last part
                 yield assigned
-            elif assigned is YES:
+            elif assigned is util.YES:
                 break
             else:
                 # we are not yet on the last part of the path
@@ -266,7 +267,7 @@ def _arguments_infer_argname(self, name, context):
     # arguments information may be missing, in which case we can't do anything
     # more
     if not (self.args or self.vararg or self.kwarg):
-        yield YES
+        yield util.YES
         return
     # first argument of instance/class method
     if self.args and getattr(self.args[0], 'name', None) == name:
@@ -293,9 +294,9 @@ def _arguments_infer_argname(self, name, context):
         context = copy_context(context)
         for infered in self.default_value(name).infer(context):
             yield infered
-        yield YES
+        yield util.YES
     except NoDefault:
-        yield YES
+        yield util.YES
 
 
 def arguments_assigned_stmts(self, node, context, asspath=None):
@@ -335,7 +336,7 @@ def _resolve_asspart(parts, asspath, context):
                 # we achieved to resolved the assignment path, don't infer the
                 # last part
                 yield assigned
-            elif assigned is YES:
+            elif assigned is util.YES:
                 return
             else:
                 # we are not yet on the last part of the path search on each
@@ -458,11 +459,11 @@ def starred_assigned_stmts(self, node=None, context=None, asspath=None):
         try:
             rhs = next(value.infer(context))
         except InferenceError:
-            yield YES
+            yield util.YES
             return
-        if rhs is YES or not hasattr(rhs, 'elts'):
+        if rhs is util.YES or not hasattr(rhs, 'elts'):
             # Not interested in inferred values without elts.
-            yield YES
+            yield util.YES
             return
 
         elts = collections.deque(rhs.elts[:])
diff --git a/astroid/scoped_nodes.py b/astroid/scoped_nodes.py
index e428f03..348278a 100644
--- a/astroid/scoped_nodes.py
+++ b/astroid/scoped_nodes.py
@@ -36,6 +36,7 @@ from astroid import manager
 from astroid import mixins
 from astroid import node_classes
 from astroid import decorators as decorators_mod
+from astroid import util
 
 
 BUILTINS = six.moves.builtins.__name__
@@ -537,7 +538,7 @@ class DictComp(ComprehensionScope):
         self.generators = []
 
     def bool_value(self):
-        return bases.YES
+        return util.YES
 
 
 class SetComp(ComprehensionScope):
@@ -549,7 +550,7 @@ class SetComp(ComprehensionScope):
         self.generators = []
 
     def bool_value(self):
-        return bases.YES
+        return util.YES
 
 
 class _ListComp(bases.NodeNG):
@@ -559,7 +560,7 @@ class _ListComp(bases.NodeNG):
     generators = None
 
     def bool_value(self):
-        return bases.YES
+        return util.YES
 
 
 if six.PY3:
@@ -885,7 +886,7 @@ class Function(bases.Statement, Lambda):
                 c.hide = True
                 c.parent = self
                 class_bases = [next(b.infer(context)) for b in caller.args[1:]]
-                c.bases = [base for base in class_bases if base != bases.YES]
+                c.bases = [base for base in class_bases if base != util.YES]
                 c._metaclass = metaclass
                 yield c
                 return
@@ -898,7 +899,7 @@ class Function(bases.Statement, Lambda):
                     for infered in returnnode.value.infer(context):
                         yield infered
                 except exceptions.InferenceError:
-                    yield bases.YES
+                    yield util.YES
 
     def bool_value(self):
         return True
@@ -935,7 +936,7 @@ def _is_metaclass(klass, seen=None):
                 if isinstance(baseobj, bases.Instance):
                     # not abstract
                     return False
-                if baseobj is bases.YES:
+                if baseobj is util.YES:
                     continue
                 if baseobj is klass:
                     continue
@@ -1089,7 +1090,7 @@ class Class(bases.Statement, LocalsDictNodeNG, mixins.FilterStmtsMixin):
                 isinstance(name_node.value, six.string_types)):
             name = name_node.value
         else:
-            return bases.YES
+            return util.YES
 
         result = Class(name, None)
 
@@ -1101,7 +1102,7 @@ class Class(bases.Statement, LocalsDictNodeNG, mixins.FilterStmtsMixin):
             # There is currently no AST node that can represent an 'unknown'
             # node (YES is not an AST node), therefore we simply return YES here
             # although we know at least the name of the class.
-            return bases.YES
+            return util.YES
 
         # Get the members of the class
         try:
@@ -1368,13 +1369,13 @@ class Class(bases.Statement, LocalsDictNodeNG, mixins.FilterStmtsMixin):
                     except exceptions.NotFoundError:
                         yield infered
                     else:
-                        yield bases.YES
+                        yield util.YES
                 else:
                     yield function_to_method(infered, self)
         except exceptions.NotFoundError:
             if not name.startswith('__') and self.has_dynamic_getattr(context):
                 # class handle some dynamic attributes, return a YES object
-                yield bases.YES
+                yield util.YES
             else:
                 raise exceptions.InferenceError(name)
 
@@ -1455,7 +1456,7 @@ class Class(bases.Statement, LocalsDictNodeNG, mixins.FilterStmtsMixin):
             # Expects this from Py3k TreeRebuilder
             try:
                 return next(node for node in self._metaclass.infer()
-                            if node is not bases.YES)
+                            if node is not util.YES)
             except (exceptions.InferenceError, StopIteration):
                 return None
         if six.PY3:
@@ -1478,7 +1479,7 @@ class Class(bases.Statement, LocalsDictNodeNG, mixins.FilterStmtsMixin):
             infered = next(assignment.infer())
         except exceptions.InferenceError:
             return
-        if infered is bases.YES: # don't expose this
+        if infered is util.YES: # don't expose this
             return None
         return infered
 
@@ -1529,7 +1530,7 @@ class Class(bases.Statement, LocalsDictNodeNG, mixins.FilterStmtsMixin):
                 values = [item[0] for item in slots.items]
             else:
                 values = slots.itered()
-            if values is bases.YES:
+            if values is util.YES:
                 continue
             if not values:
                 # Stop the iteration, because the class
@@ -1539,7 +1540,7 @@ class Class(bases.Statement, LocalsDictNodeNG, mixins.FilterStmtsMixin):
             for elt in values:
                 try:
                     for infered in elt.infer():
-                        if infered is bases.YES:
+                        if infered is util.YES:
                             continue
                         if (not isinstance(infered, node_classes.Const) or
                                 not isinstance(infered.value,
diff --git a/astroid/tests/unittest_brain.py b/astroid/tests/unittest_brain.py
index 8dfa300..4475819 100644
--- a/astroid/tests/unittest_brain.py
+++ b/astroid/tests/unittest_brain.py
@@ -25,6 +25,7 @@ from astroid import bases
 from astroid import builder
 from astroid import nodes
 from astroid import test_utils
+from astroid import util
 import astroid
 
 
@@ -105,7 +106,7 @@ class NamedTupleTest(unittest.TestCase):
         def foo(fields):
            return __(namedtuple("foo", fields))
         """)
-        self.assertIs(bases.YES, next(klass.infer()))
+        self.assertIs(util.YES, next(klass.infer()))
 
     @unittest.skipIf(sys.version_info[0] > 2,
                      'namedtuple inference is broken on Python 3')
diff --git a/astroid/tests/unittest_builder.py b/astroid/tests/unittest_builder.py
index e4d5866..87e90e7 100644
--- a/astroid/tests/unittest_builder.py
+++ b/astroid/tests/unittest_builder.py
@@ -29,6 +29,7 @@ from astroid import exceptions
 from astroid import manager
 from astroid import nodes
 from astroid import test_utils
+from astroid import util
 from astroid.tests import resources
 
 MANAGER = manager.AstroidManager()
@@ -482,7 +483,7 @@ class BuilderTest(unittest.TestCase):
         n = test_utils.get_name_node(astroid, 'n')
         self.assertIsNot(n.scope(), astroid)
         self.assertEqual([i.__class__ for i in n.infer()],
-                         [bases.YES.__class__])
+                         [util.YES.__class__])
 
     def test_no_future_imports(self):
         mod = builder.parse("import sys")
diff --git a/astroid/tests/unittest_helpers.py b/astroid/tests/unittest_helpers.py
index a69c136..dfe5b60 100644
--- a/astroid/tests/unittest_helpers.py
+++ b/astroid/tests/unittest_helpers.py
@@ -27,6 +27,7 @@ from astroid import helpers
 from astroid import manager

 from astroid import raw_building

 from astroid import test_utils

+from astroid import util

 

 

 class TestHelpers(unittest.TestCase):

@@ -154,7 +155,7 @@ class TestHelpers(unittest.TestCase):
         from unknown import Unknown

         u = Unknown #@

         ''')

-        self.assertEqual(helpers.object_type(node), bases.YES)

+        self.assertEqual(helpers.object_type(node), util.YES)

 

     def test_object_type_too_many_types(self):

         node = test_utils.extract_node('''

@@ -166,7 +167,7 @@ class TestHelpers(unittest.TestCase):
                 return 1

         test(Unknown) #@

         ''')

-        self.assertEqual(helpers.object_type(node), bases.YES)

+        self.assertEqual(helpers.object_type(node), util.YES)

 

     def test_is_subtype(self):

         ast_nodes = test_utils.extract_node('''

@@ -216,8 +217,8 @@ class TestHelpers(unittest.TestCase):
         class F(D, E): pass #@

         ''')

         self.assertFalse(helpers.is_subtype(cls_e, cls_f))

-        self.assertEqual(helpers.is_subtype(cls_f, cls_e), bases.YES)

-        self.assertEqual(helpers.is_supertype(cls_e, cls_f), bases.YES)

+        self.assertEqual(helpers.is_subtype(cls_f, cls_e), util.YES)

+        self.assertEqual(helpers.is_supertype(cls_e, cls_f), util.YES)

         self.assertFalse(helpers.is_supertype(cls_f, cls_e))

 

     def test_is_subtype_supertype_unknown_bases(self):

diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index b091a2b..20666f5 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -27,10 +27,11 @@ import six
 from astroid import InferenceError, builder, nodes
 from astroid.builder import parse
 from astroid.inference import infer_end as inference_infer_end
-from astroid.bases import YES, Instance, BoundMethod, UnboundMethod,\
+from astroid.bases import Instance, BoundMethod, UnboundMethod,\
                                 path_wrapper, BUILTINS
 from astroid import objects
 from astroid import test_utils
+from astroid import util
 from astroid.tests import resources
 
 
@@ -307,7 +308,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         self.assertIsInstance(obj1, nodes.Const)
         self.assertEqual(obj1.value, 0)
         obj1 = next(infered)
-        self.assertIs(obj1, YES, obj1)
+        self.assertIs(obj1, util.YES, obj1)
         self.assertRaises(StopIteration, partial(next, infered))
 
     def test_args_default_inference2(self):
@@ -316,13 +317,13 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         self.assertIsInstance(obj1, nodes.Const)
         self.assertEqual(obj1.value, 4)
         obj1 = next(infered)
-        self.assertIs(obj1, YES, obj1)
+        self.assertIs(obj1, util.YES, obj1)
         self.assertRaises(StopIteration, partial(next, infered))
 
     def test_inference_restrictions(self):
         infered = test_utils.get_name_node(self.ast['C']['meth1'], 'arg1').infer()
         obj1 = next(infered)
-        self.assertIs(obj1, YES, obj1)
+        self.assertIs(obj1, util.YES, obj1)
         self.assertRaises(StopIteration, partial(next, infered))
 
     def test_ancestors_inference(self):
@@ -544,7 +545,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ast = parse(code, __name__)
         xxx = ast['xxx']
         self.assertSetEqual({n.__class__ for n in xxx.infered()},
-                            {nodes.Const, YES.__class__})
+                            {nodes.Const, util.YES.__class__})
 
     def test_method_argument(self):
         code = '''
@@ -560,13 +561,13 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ast = parse(code, __name__)
         arg = test_utils.get_name_node(ast['ErudiEntitySchema']['__init__'], 'e_type')
         self.assertEqual([n.__class__ for n in arg.infer()],
-                         [YES.__class__])
+                         [util.YES.__class__])
         arg = test_utils.get_name_node(ast['ErudiEntitySchema']['__init__'], 'kwargs')
         self.assertEqual([n.__class__ for n in arg.infer()],
                          [nodes.Dict])
         arg = test_utils.get_name_node(ast['ErudiEntitySchema']['meth'], 'e_type')
         self.assertEqual([n.__class__ for n in arg.infer()],
-                         [YES.__class__])
+                         [util.YES.__class__])
         arg = test_utils.get_name_node(ast['ErudiEntitySchema']['meth'], 'args')
         self.assertEqual([n.__class__ for n in arg.infer()],
                          [nodes.Tuple])
@@ -704,7 +705,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         for node in ast_nodes[:3]:
             self.assertRaises(InferenceError, next, node.infer())
         for node in ast_nodes[3:]:
-            self.assertEqual(next(node.infer()), YES)
+            self.assertEqual(next(node.infer()), util.YES)
 
     def test_bytes_subscript(self):
         node = test_utils.extract_node('''b'a'[0]''')
@@ -947,7 +948,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         self.assertEqual(first.value, 43)
 
         second = next(ast_nodes[1].infer())
-        self.assertEqual(second, YES)
+        self.assertEqual(second, util.YES)
 
     def test_binary_op_other_type_using_reflected_operands(self):
         ast_nodes = test_utils.extract_node('''
@@ -958,7 +959,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         1 + A() #@
         ''')
         first = next(ast_nodes[0].infer())
-        self.assertEqual(first, YES)
+        self.assertEqual(first, util.YES)
 
         second = next(ast_nodes[1].infer())
         self.assertIsInstance(second, nodes.Const)
@@ -972,7 +973,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         1 + A() #@
         ''')
         first = next(ast_node.infer())
-        self.assertEqual(first, YES)
+        self.assertEqual(first, util.YES)
 
     def test_binary_op_list_mul(self):
         for code in ('a = [[]] * 2', 'a = 2 * [[]]'):
@@ -989,10 +990,10 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ast = builder.string_build('a = [1] * None\nb = [1] * "r"')
         infered = ast['a'].infered()
         self.assertEqual(len(infered), 1)
-        self.assertEqual(infered[0], YES)
+        self.assertEqual(infered[0], util.YES)
         infered = ast['b'].infered()
         self.assertEqual(len(infered), 1)
-        self.assertEqual(infered[0], YES)
+        self.assertEqual(infered[0], util.YES)
 
     def test_binary_op_tuple_add(self):
         ast = builder.string_build('a = (1,) + (2,)', __name__, __file__)
@@ -1039,7 +1040,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         callfuncnode = test_utils.extract_node(code)
         infered = list(callfuncnode.infer())
         self.assertEqual(len(infered), 2, infered)
-        infered.remove(YES)
+        infered.remove(util.YES)
         self.assertIsInstance(infered[0], nodes.Const)
         self.assertIsNone(infered[0].value)
 
@@ -1051,7 +1052,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ast = parse(code, __name__)
         infered = list(ast['f'].ilookup('a'))
         self.assertEqual(len(infered), 1)
-        self.assertEqual(infered[0], YES)
+        self.assertEqual(infered[0], util.YES)
 
     def test_nonregr_instance_attrs(self):
         """non regression for instance_attrs infinite loop : pylint / #4"""
@@ -1103,7 +1104,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         self.assertTrue(ast.absolute_import_activated(), True)
         infered = next(test_utils.get_name_node(ast, 'import_package_subpackage_module').infer())
         # failed to import since absolute_import is activated
-        self.assertIs(infered, YES)
+        self.assertIs(infered, util.YES)
 
     def test_nonregr_absolute_import(self):
         ast = resources.build_file('data/absimp/string.py', 'data.absimp.string')
@@ -1221,7 +1222,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ast = parse(code, __name__)
         infered = list(test_utils.get_name_node(ast['foo'], 'spam').infer())
         self.assertEqual(len(infered), 1)
-        self.assertIs(infered[0], YES)
+        self.assertIs(infered[0], util.YES)
 
     def test_nonregr_func_global(self):
         code = '''
@@ -1412,7 +1413,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ast = parse(code, __name__)
         sub = ast['sub'].infered()[0]
         mul = ast['mul'].infered()[0]
-        self.assertIs(sub, YES)
+        self.assertIs(sub, util.YES)
         self.assertIsInstance(mul, nodes.Const)
         self.assertEqual(mul.value, 42)
 
@@ -1431,7 +1432,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ast = parse(code, __name__)
         sub = ast['sub'].infered()[0]
         mul = ast['mul'].infered()[0]
-        self.assertIs(sub, YES)
+        self.assertIs(sub, util.YES)
         self.assertIsInstance(mul, nodes.Const)
         self.assertEqual(mul.value, 42)
 
@@ -1451,7 +1452,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         ast = parse(code, __name__)
         sub = ast['sub'].infered()[0]
         mul = ast['mul'].infered()[0]
-        self.assertIs(sub, YES)
+        self.assertIs(sub, util.YES)
         self.assertIsInstance(mul, nodes.List)
         self.assertIsInstance(mul.elts[0], nodes.Const)
         self.assertEqual(mul.elts[0].value, 42)
@@ -1468,12 +1469,12 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         """
         ast = parse(code, __name__)
         node = ast['c']
-        self.assertEqual(node.infered(), [YES])
+        self.assertEqual(node.infered(), [util.YES])
 
     def test_infer_empty_nodes(self):
         # Should not crash when trying to infer EmptyNodes.
         node = nodes.EmptyNode()
-        self.assertEqual(node.infered(), [YES])
+        self.assertEqual(node.infered(), [util.YES])
 
     def test_infinite_loop_for_decorators(self):
         # Issue https://bitbucket.org/logilab/astroid/issue/50
@@ -1941,7 +1942,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
 
     def test_unary_op_leaks_stop_iteration(self):
         node = test_utils.extract_node('+[] #@')
-        self.assertEqual(YES, next(node.infer()))
+        self.assertEqual(util.YES, next(node.infer()))
 
     def test_unary_operands(self):
         ast_nodes = test_utils.extract_node('''
@@ -1992,7 +1993,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
 
         for bad_node in ast_nodes[4:]:
             inferred = next(bad_node.infer())
-            self.assertEqual(inferred, YES)
+            self.assertEqual(inferred, util.YES)
 
     def test_binary_op_type_errors(self):
         ast_nodes = test_utils.extract_node('''
@@ -2181,11 +2182,11 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         genexpr = next(module['genexpr'].infer())
         self.assertTrue(genexpr.bool_value())
         dict_comp = next(module['dict_comp'].infer())
-        self.assertEqual(dict_comp, YES)
+        self.assertEqual(dict_comp, util.YES)
         set_comp = next(module['set_comp'].infer())
-        self.assertEqual(set_comp, YES)
+        self.assertEqual(set_comp, util.YES)
         list_comp = next(module['list_comp'].infer())
-        self.assertEqual(list_comp, YES)
+        self.assertEqual(list_comp, util.YES)
         lambda_func = next(module['lambda_func'].infer())
         self.assertTrue(lambda_func)
         unbound_method = next(module['unbound_method'].infer())
@@ -2199,13 +2200,13 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         bin_op = module['bin_op'].parent.value
         self.assertTrue(bin_op.bool_value())
         bool_op = module['bool_op'].parent.value
-        self.assertEqual(bool_op.bool_value(), YES)
+        self.assertEqual(bool_op.bool_value(), util.YES)
         callfunc = module['callfunc'].parent.value
-        self.assertEqual(callfunc.bool_value(), YES)
+        self.assertEqual(callfunc.bool_value(), util.YES)
         good_callfunc = next(module['good_callfunc'].infer())
         self.assertTrue(good_callfunc.bool_value())
         compare = module['compare'].parent.value
-        self.assertEqual(compare.bool_value(), YES)
+        self.assertEqual(compare.bool_value(), util.YES)
 
     def test_bool_value_instances(self):
         instances = test_utils.extract_node('''
@@ -2238,7 +2239,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         AlwaysTrueInstance() #@
         ErrorInstance() #@
         '''.format(bool=BOOL_SPECIAL_METHOD))
-        expected = (False, True, False, True, True, YES, YES)
+        expected = (False, True, False, True, True, util.YES, util.YES)
         for node, expected_value in zip(instances, expected):
             inferred = next(node.infer())
             self.assertEqual(inferred.bool_value(), expected_value)
@@ -2310,7 +2311,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         A() + B() #@
         ''')
         inferred = next(node.infer())
-        self.assertEqual(inferred, YES)
+        self.assertEqual(inferred, util.YES)
 
     def test_binop_different_types_reflected_and_normal_not_implemented(self):
         node = test_utils.extract_node('''
@@ -2321,7 +2322,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         A() + B() #@
         ''')
         inferred = next(node.infer())
-        self.assertEqual(inferred, YES)
+        self.assertEqual(inferred, util.YES)
 
     def test_binop_subtype(self):
         node = test_utils.extract_node('''
@@ -2354,7 +2355,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         B() + A() #@
         ''')
         inferred = next(node.infer())
-        self.assertEqual(inferred, YES)
+        self.assertEqual(inferred, util.YES)
 
     def test_binop_supertype(self):
         node = test_utils.extract_node('''
@@ -2393,7 +2394,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         A() + B() #@
         ''')
         inferred = next(node.infer())
-        self.assertEqual(inferred, YES)
+        self.assertEqual(inferred, util.YES)
 
     def test_binop_inferrence_errors(self):
         ast_nodes = test_utils.extract_node('''
@@ -2408,7 +2409,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         A() + B() #@
         ''')
         for node in ast_nodes:
-            self.assertEqual(next(node.infer()), YES)
+            self.assertEqual(next(node.infer()), util.YES)
 
     def test_binop_ambiguity(self):
         ast_nodes = test_utils.extract_node('''
@@ -2431,7 +2432,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         C() + A() #@
         ''')
         for node in ast_nodes:
-            self.assertEqual(next(node.infer()), YES)
+            self.assertEqual(next(node.infer()), util.YES)
 
     def test_bin_op_supertype_more_complicated_example(self):
         ast_node = test_utils.extract_node('''
@@ -2460,7 +2461,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
             def __add__(self, other): return NotImplemented
         A() + A() #@        
         ''')
-        self.assertEqual(next(ast_node.infer()), YES)
+        self.assertEqual(next(ast_node.infer()), util.YES)
 
     def test_aug_op_same_type_aug_implemented(self):
         ast_node = test_utils.extract_node('''
@@ -2495,7 +2496,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         b = B()
         b+=A() #@
         ''')
-        self.assertEqual(next(ast_node.infer()), YES)
+        self.assertEqual(next(ast_node.infer()), util.YES)
 
     def test_aug_op_subtype_aug_op_is_implemented(self):
         ast_node = test_utils.extract_node('''
@@ -2530,7 +2531,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         f = A()
         f += B() #@
         ''')
-        self.assertEqual(next(ast_node.infer()), YES)
+        self.assertEqual(next(ast_node.infer()), util.YES)
 
     def test_aug_different_types_augop_implemented(self):
         ast_node = test_utils.extract_node('''
@@ -2578,7 +2579,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         a = A()
         a += B() #@
         ''')
-        self.assertEqual(next(ast_node.infer()), YES)
+        self.assertEqual(next(ast_node.infer()), util.YES)
 
     def test_augop_supertypes_not_implemented_returned_for_all(self):
         ast_node = test_utils.extract_node('''
@@ -2590,7 +2591,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         a = A()
         a += B() #@
         ''')
-        self.assertEqual(next(ast_node.infer()), YES)
+        self.assertEqual(next(ast_node.infer()), util.YES)
 
     def test_augop_supertypes_augop_implemented(self):
         ast_node = test_utils.extract_node('''
@@ -2662,7 +2663,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
                          [1, 2, 1, 2])
         for rest in ast_nodes[1:]:
             inferred = next(rest.infer())
-            self.assertEqual(inferred, YES)
+            self.assertEqual(inferred, util.YES)
 
     def test_special_method_masquerading_as_another(self):
         ast_node = test_utils.extract_node('''
@@ -2694,7 +2695,7 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
 
 class GetattrTest(unittest.TestCase):
 
-    def test_yes(self):
+    def test_yes_when_unknown(self):
         ast_nodes = test_utils.extract_node('''
         from missing import Missing
         getattr(1, Unknown) #@
@@ -2712,7 +2713,7 @@ class GetattrTest(unittest.TestCase):
 
         for node in ast_nodes[4:]:
             inferred = next(node.infer())
-            self.assertEqual(inferred, YES, node)
+            self.assertEqual(inferred, util.YES, node)
 
     def test_attrname_not_string(self):
         ast_nodes = test_utils.extract_node('''
@@ -2809,7 +2810,7 @@ class HasattrTest(unittest.TestCase):
         ''')
         for node in ast_nodes:
             inferred = next(node.infer())
-            self.assertEqual(inferred, YES)
+            self.assertEqual(inferred, util.YES)
 
     def test_attribute_is_missing(self):
         ast_nodes = test_utils.extract_node('''
@@ -2882,7 +2883,7 @@ class BoolOpTest(unittest.TestCase):
         ''')
         for node in ast_nodes:
             inferred = next(node.infer())
-            self.assertEqual(inferred, YES)
+            self.assertEqual(inferred, util.YES)
 
     def test_other_nodes(self):
         ast_nodes = test_utils.extract_node('''
@@ -2962,7 +2963,7 @@ class TestCallable(unittest.TestCase):
         ''')
         for node in ast_nodes:
             inferred = next(node.infer())
-            self.assertEqual(inferred, YES)
+            self.assertEqual(inferred, util.YES)
 
     def test_not_callable(self):
         ast_nodes = test_utils.extract_node('''
@@ -2988,12 +2989,12 @@ class TestBool(unittest.TestCase):
             ('bool(True)', True),
             ('bool(False)', False),
             ('bool(None)', False),
-            ('from unknown import Unknown; __(bool(Unknown))', YES),
+            ('from unknown import Unknown; __(bool(Unknown))', util.YES),
         ]
         for code, expected in pairs:
             node = test_utils.extract_node(code)
             inferred = next(node.infer())
-            if expected is YES:
+            if expected is util.YES:
                 self.assertEqual(expected, inferred)
             else:
                 self.assertEqual(inferred.value, expected)
diff --git a/astroid/tests/unittest_lookup.py b/astroid/tests/unittest_lookup.py
index 491ae78..17c8ba4 100644
--- a/astroid/tests/unittest_lookup.py
+++ b/astroid/tests/unittest_lookup.py
@@ -27,6 +27,7 @@ from astroid import exceptions
 from astroid import nodes
 from astroid import scoped_nodes
 from astroid import test_utils
+from astroid import util
 from astroid.tests import resources
 
 
@@ -172,7 +173,7 @@ class LookupTest(resources.SysPathSetup, unittest.TestCase):
         """)
         var = astroid.body[1].value
         if sys.version_info < (3, 0):
-            self.assertEqual(var.infered(), [bases.YES])
+            self.assertEqual(var.infered(), [util.YES])
         else:
             self.assertRaises(exceptions.UnresolvableName, var.infered)
 
diff --git a/astroid/tests/unittest_nodes.py b/astroid/tests/unittest_nodes.py
index 2a08843..ff2468b 100644
--- a/astroid/tests/unittest_nodes.py
+++ b/astroid/tests/unittest_nodes.py
@@ -29,6 +29,7 @@ from astroid import builder
 from astroid import exceptions
 from astroid import node_classes
 from astroid import nodes
+from astroid import util
 from astroid import test_utils
 from astroid.tests import resources
 
@@ -369,7 +370,7 @@ from ..cave import wine\n\n"""
         # present in the other version.
         self.assertIsInstance(excs[0], nodes.Class)
         self.assertEqual(excs[0].name, 'PickleError')
-        self.assertIs(excs[-1], bases.YES)
+        self.assertIs(excs[-1], util.YES)
 
     def test_absolute_import(self):
         astroid = resources.build_file('data/absimport.py')
diff --git a/astroid/tests/unittest_protocols.py b/astroid/tests/unittest_protocols.py
index 1d2e380..30b5f94 100644
--- a/astroid/tests/unittest_protocols.py
+++ b/astroid/tests/unittest_protocols.py
@@ -18,10 +18,10 @@
 
 import unittest
 
-from astroid import YES
 from astroid.test_utils import extract_node, require_version
 from astroid import InferenceError
 from astroid import nodes
+from astroid import util
 from astroid.node_classes import AssName, Const, Name, Starred
 
 
@@ -67,7 +67,7 @@ class ProtocolTests(unittest.TestCase):
 
         for1_starred = next(assign_stmts.nodes_of_class(Starred))
         assigned = next(for1_starred.assigned_stmts())
-        self.assertEqual(assigned, YES)
+        self.assertEqual(assigned, util.YES)
 
     def _get_starred_stmts(self, code):
         assign_stmt = extract_node("{} #@".format(code))
@@ -108,16 +108,16 @@ class ProtocolTests(unittest.TestCase):
     @require_version(minver='3.0')
     def test_assigned_stmts_starred_yes(self):
         # Not something iterable and known
-        self._helper_starred_expected("a, *b = range(3) #@", YES)
+        self._helper_starred_expected("a, *b = range(3) #@", util.YES)
         # Not something inferrable
-        self._helper_starred_expected("a, *b = balou() #@", YES)
+        self._helper_starred_expected("a, *b = balou() #@", util.YES)
         # In function, unknown.
         self._helper_starred_expected("""
         def test(arg):
-            head, *tail = arg #@""", YES)
+            head, *tail = arg #@""", util.YES)
         # These cases aren't worth supporting.
         self._helper_starred_expected(
-            "a, (*b, c), d = (1, (2, 3, 4), 5) #@", YES)
+            "a, (*b, c), d = (1, (2, 3, 4), 5) #@", util.YES)
 
     @require_version(minver='3.0')
     def test_assign_stmts_starred_fails(self):
diff --git a/astroid/tests/unittest_scoped_nodes.py b/astroid/tests/unittest_scoped_nodes.py
index 05425b2..17bb70e 100644
--- a/astroid/tests/unittest_scoped_nodes.py
+++ b/astroid/tests/unittest_scoped_nodes.py
@@ -24,7 +24,10 @@ from functools import partial
 import unittest
 import warnings
 
-from astroid import YES, builder, nodes, scoped_nodes
+from astroid import builder
+from astroid import nodes
+from astroid import scoped_nodes
+from astroid import util
 from astroid.exceptions import (
     InferenceError, NotFoundError,
     NoDefault, ResolveError, MroError,
@@ -1088,7 +1091,7 @@ class ClassNodeTest(ModuleLoader, unittest.TestCase):
         instance = astroid['tgts']
         # used to raise "'_Yes' object is not iterable", see
         # https://bitbucket.org/logilab/astroid/issue/17
-        self.assertEqual(list(instance.infer()), [YES])
+        self.assertEqual(list(instance.infer()), [util.YES])
 
     def test_slots(self):
         astroid = builder.parse("""
@@ -1352,7 +1355,7 @@ class ClassNodeTest(ModuleLoader, unittest.TestCase):
         class B(object): pass 
         ''')
         cls = module['B']
-        self.assertEqual(YES, next(cls.igetattr('foo')))
+        self.assertEqual(util.YES, next(cls.igetattr('foo')))
 
     def test_metaclass_lookup(self):
         module = builder.parse('''
diff --git a/astroid/util.py b/astroid/util.py
new file mode 100644
index 0000000..8dde9b9
--- /dev/null
+++ b/astroid/util.py
@@ -0,0 +1,38 @@
+# copyright 2003-2015 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
+# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
+#
+# This file is part of astroid.
+#
+# astroid 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.
+#
+# astroid 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 astroid. If not, see <http://www.gnu.org/licenses/>.
+#
+# The code in this file was originally part of logilab-common, licensed under
+# the same license.
+
+class _Yes(object):
+    """Special inference object, which is returned when inference fails."""
+    def __repr__(self):
+        return 'YES'
+
+    def __getattribute__(self, name):
+        if name == 'next':
+            raise AttributeError('next method should not be called')
+        if name.startswith('__') and name.endswith('__'):
+            return super(_Yes, self).__getattribute__(name)
+        return self
+
+    def __call__(self, *args, **kwargs):
+        return self
+
+
+YES = _Yes()