allow_none=False for all trait types but Instance and Type

IPython/utils/tests/test_traitlets.py

@@ -998,8 +998,8 b' class TestInstanceList(TraitTestBase):'
         self.assertIs(self.obj.traits()['value']._trait.klass, Foo)
 
     _default_value = []
-    _good_values = [[Foo(), Foo(), None], None]
-    _bad_values = [['1', 2,], '1', [Foo]]
+    _good_values = [[Foo(), Foo(), None], []]
+    _bad_values = [['1', 2,], '1', [Foo], None]
 
 class UnionListTrait(HasTraits):
 
@@ -1475,14 +1475,14 b' class TestForwardDeclaredInstanceList(TraitTestBase):'
         [ForwardDeclaredBar(), ForwardDeclaredBarSub(), None],
         [None],
         [],
-        None,
     ]
     _bad_values = [
         ForwardDeclaredBar(),
         [ForwardDeclaredBar(), 3],
         '1',
         # Note that this is the type, not an instance.
-        [ForwardDeclaredBar]
+        [ForwardDeclaredBar],
+        None,
     ]
 
 class TestForwardDeclaredTypeList(TraitTestBase):
@@ -1498,14 +1498,14 b' class TestForwardDeclaredTypeList(TraitTestBase):'
         [ForwardDeclaredBar, ForwardDeclaredBarSub, None],
         [],
         [None],
-        None,
     ]
     _bad_values = [
         ForwardDeclaredBar,
         [ForwardDeclaredBar, 3],
         '1',
         # Note that this is an instance, not the type.
-        [ForwardDeclaredBar()]
+        [ForwardDeclaredBar()],
+        None,
     ]
 ###
 # End Forward Declaration Tests

IPython/utils/traitlets.py

@@ -1340,9 +1340,9 b' class CBool(Bool):'
 class Enum(TraitType):
     """An enum that whose value must be in a given sequence."""
 
-    def __init__(self, values, default_value=None, allow_none=True, **metadata):
+    def __init__(self, values, default_value=None, **metadata):
         self.values = values
-        super(Enum, self).__init__(default_value, allow_none=allow_none, **metadata)
+        super(Enum, self).__init__(default_value, **metadata)
 
     def validate(self, obj, value):
         if value in self.values:
@@ -1378,7 +1378,7 b' class Container(Instance):'
     _valid_defaults = SequenceTypes
     _trait = None
 
-    def __init__(self, trait=None, default_value=None, allow_none=True,
+    def __init__(self, trait=None, default_value=None, allow_none=False,
                 **metadata):
         """Create a container trait type from a list, set, or tuple.
 
@@ -1474,8 +1474,7 b' class List(Container):'
     klass = list
     _cast_types = (tuple,)
 
-    def __init__(self, trait=None, default_value=None, minlen=0, maxlen=sys.maxsize,
-                allow_none=True, **metadata):
+    def __init__(self, trait=None, default_value=None, minlen=0, maxlen=sys.maxsize, **metadata):
         """Create a List trait type from a list, set, or tuple.
 
         The default value is created by doing ``List(default_value)``,
@@ -1516,7 +1515,7 b' class List(Container):'
         self._minlen = minlen
         self._maxlen = maxlen
         super(List, self).__init__(trait=trait, default_value=default_value,
-                                allow_none=allow_none, **metadata)
+                                **metadata)
 
     def length_error(self, obj, value):
         e = "The '%s' trait of %s instance must be of length %i <= L <= %i, but a value of %s was specified." \
@@ -1550,7 +1549,7 b' class Tuple(Container):'
     _cast_types = (list,)
 
     def __init__(self, *traits, **metadata):
-        """Tuple(*traits, default_value=None, allow_none=True, **medatata)
+        """Tuple(*traits, default_value=None, **medatata)
 
         Create a tuple from a list, set, or tuple.
 
@@ -1612,8 +1611,7 b' class Tuple(Container):'
         if self._traits and default_value is None:
             # don't allow default to be an empty container if length is specified
             args = None
-        super(Container,self).__init__(klass=self.klass, args=args,
-                                  allow_none=allow_none, **metadata)
+        super(Container,self).__init__(klass=self.klass, args=args, **metadata)
 
     def validate_elements(self, obj, value):
         if not self._traits:
@@ -1646,7 +1644,7 b' class Tuple(Container):'
 class Dict(Instance):
     """An instance of a Python dict."""
 
-    def __init__(self, default_value={}, allow_none=True, **metadata):
+    def __init__(self, default_value={}, allow_none=False, **metadata):
         """Create a dict trait type from a dict.
 
         The default value is created by doing ``dict(default_value)``,
@@ -1668,7 +1666,7 b' class Dict(Instance):'
 class EventfulDict(Instance):
     """An instance of an EventfulDict."""
 
-    def __init__(self, default_value={}, allow_none=True, **metadata):
+    def __init__(self, default_value={}, allow_none=False, **metadata):
         """Create a EventfulDict trait type from a dict.
 
         The default value is created by doing
@@ -1691,7 +1689,7 b' class EventfulDict(Instance):'
 class EventfulList(Instance):
     """An instance of an EventfulList."""
 
-    def __init__(self, default_value=None, allow_none=True, **metadata):
+    def __init__(self, default_value=None, allow_none=False, **metadata):
         """Create a EventfulList trait type from a dict.
 
         The default value is created by doing