diff --git a/holoviews/__init__.py b/holoviews/__init__.py
index 70109b2013..22c241d7ce 100644
--- a/holoviews/__init__.py
+++ b/holoviews/__init__.py
@@ -10,14 +10,15 @@
                                         reponame="holoviews"))
 
 from .core import archive, config                        # noqa (API import)
-from .core.dimension import OrderedDict, Dimension       # noqa (API import)
 from .core.boundingregion import BoundingBox             # noqa (API import)
+from .core.dimension import OrderedDict, Dimension       # noqa (API import)
+from .core.element import Element, Collator              # noqa (API import)
+from .core.layout import (Layout, NdLayout, Empty,       # noqa (API import)
+                          AdjointLayout)
+from .core.ndmapping import NdMapping                    # noqa (API import)
 from .core.options import (Options, Store, Cycle,        # noqa (API import)
                            Palette, StoreOptions)
-from .core.layout import *                               # noqa (API import)
-from .core.element import *                              # noqa (API import)
-from .core.overlay import *                              # noqa (API import)
-from .core.tree import *                                 # noqa (API import)
+from .core.overlay import Overlay, NdOverlay             # noqa (API import)
 from .core.spaces import (HoloMap, Callable, DynamicMap, # noqa (API import)
                           GridSpace, GridMatrix)
 
@@ -82,3 +83,7 @@ def help(obj, visualization=True, ansi=True, backend=None,
         print((msg if visualization is False else '') + info)
     else:
         pydoc.help(obj)
+
+
+del (absolute_import, code, f, filename, np, os, print_function, pydoc,
+     rcfile, warnings)
diff --git a/holoviews/core/element.py b/holoviews/core/element.py
index f9a493a4be..4281c2c707 100644
--- a/holoviews/core/element.py
+++ b/holoviews/core/element.py
@@ -22,6 +22,8 @@ class Element(ViewableElement, Composable, Overlayable):
 
     group = param.String(default='Element', constant=True)
 
+    __abstract = True
+
     def hist(self, dimension=None, num_bins=20, bin_range=None,
              adjoin=True, **kwargs):
         """
@@ -261,6 +263,8 @@ class Element2D(Element):
         Allows overriding the extents of the Element in 2D space defined
         as four-tuple defining the (left, bottom, right and top) edges.""")
 
+    __abstract = True
+
 
 class Element3D(Element2D):
 
@@ -268,6 +272,8 @@ class Element3D(Element2D):
         Allows overriding the extents of the Element in 3D space
         defined as (xmin, ymin, zmin, xmax, ymax, zmax).""")
 
+    __abstract = True
+
 
 class Collator(NdMapping):
     """
diff --git a/holoviews/core/ndmapping.py b/holoviews/core/ndmapping.py
index 761c9b6b10..5de4d9dab3 100644
--- a/holoviews/core/ndmapping.py
+++ b/holoviews/core/ndmapping.py
@@ -717,7 +717,7 @@ class UniformNdMapping(NdMapping):
 
     data_type = (ViewableElement, NdMapping)
 
-    _abstract = True
+    __abstract = True
     _deep_indexable = True
     _auxiliary_component = False
 
diff --git a/holoviews/element/__init__.py b/holoviews/element/__init__.py
index 6cb1b6691f..1d798164ce 100644
--- a/holoviews/element/__init__.py
+++ b/holoviews/element/__init__.py
@@ -110,7 +110,7 @@ def table(self, kdims=None, vdims=None, groupby=None, **kwargs):
 
 
 def public(obj):
-    if not isinstance(obj, type) or getattr(obj, 'abstract', False):
+    if not isinstance(obj, type) or getattr(obj, 'abstract', False) and not obj is Element:
         return False
     return issubclass(obj, Element)
 
diff --git a/holoviews/tests/core/testoptions.py b/holoviews/tests/core/testoptions.py
index 24465a8cd0..90f1bf5231 100644
--- a/holoviews/tests/core/testoptions.py
+++ b/holoviews/tests/core/testoptions.py
@@ -1,8 +1,10 @@
 import os
 import pickle
 import numpy as np
-from holoviews import Store, StoreOptions, Histogram, Image
-from holoviews.core.options import OptionError, Cycle, Options, OptionTree, options_policy
+from holoviews import Store, Histogram, Image
+from holoviews.core.options import (
+    OptionError, Cycle, Options, OptionTree, StoreOptions, options_policy
+)
 from holoviews.element.comparison import ComparisonTestCase
 from holoviews import plotting              # noqa Register backends
 from unittest import SkipTest