diff --git a/draftjs_exporter/constants.py b/draftjs_exporter/constants.py
index 882f5ee..8e6e18a 100644
--- a/draftjs_exporter/constants.py
+++ b/draftjs_exporter/constants.py
@@ -3,10 +3,13 @@ from __future__ import absolute_import, unicode_literals
 
 # http://stackoverflow.com/a/22723724/1798491
 class Enum(object):
-    def __init__(self, tupleList):
-        self.tupleList = tupleList
+    def __init__(self, *elements):
+        self.elements = tuple(elements)
 
     def __getattr__(self, name):
+        if name not in self.elements:
+            raise AttributeError("'Enum' has no attribute '{}'".format(name))
+
         return name
 
 
@@ -27,6 +30,6 @@ class BLOCK_TYPES:
     ATOMIC = 'atomic'
     HORIZONTAL_RULE = 'horizontal-rule'
 
-ENTITY_TYPES = Enum(('LINK', 'IMAGE', 'TOKEN'))
+ENTITY_TYPES = Enum('LINK', 'IMAGE', 'TOKEN')
 
-INLINE_STYLES = Enum(('BOLD', 'CODE', 'ITALIC', 'STRIKETHROUGH', 'UNDERLINE'))
+INLINE_STYLES = Enum('BOLD', 'CODE', 'ITALIC', 'STRIKETHROUGH', 'UNDERLINE')
diff --git a/draftjs_exporter/dom.py b/draftjs_exporter/dom.py
index 0b76d7b..89ab65d 100644
--- a/draftjs_exporter/dom.py
+++ b/draftjs_exporter/dom.py
@@ -13,11 +13,11 @@ except NameError:
     unicode = lambda s: str(s)
 
 
-def Soup(str):
+def Soup(raw_str):
     """
     Wrapper around BeautifulSoup to keep the code DRY.
     """
-    return BeautifulSoup(str, 'html5lib')
+    return BeautifulSoup(raw_str, 'html5lib')
 
 
 class DOM(object):
@@ -25,11 +25,14 @@ class DOM(object):
     Wrapper around our HTML building library to facilitate changes.
     """
     @staticmethod
-    def create_tag(type, attributes={}):
-        return Soup('').new_tag(type, **attributes)
+    def create_tag(type_, attributes=None):
+        if attributes is None:
+            attributes = {}
+
+        return Soup('').new_tag(type_, **attributes)
 
     @staticmethod
-    def create_element(type=None, props={}, *children):
+    def create_element(type_=None, props=None, *children):
         """
         Signature inspired by React.createElement.
         createElement(
@@ -39,15 +42,17 @@ class DOM(object):
         )
         https://facebook.github.io/react/docs/top-level-api.html#react.createelement
         """
-        if not type:
+        if props is None:
+            props = {}
+
+        if not type_:
             elt = DOM.create_document_fragment()
         else:
             attributes = {}
 
             # Map props from React/Draft.js to HTML lingo.
             if 'className' in props:
-                props['class'] = props.get('className')
-                props.pop('className', None)
+                props['class'] = props.pop('className')
 
             for key in props:
                 prop = props[key]
@@ -56,10 +61,10 @@ class DOM(object):
                     attributes[key] = prop
 
             # "type" is either an entity with a render method, or a tag name.
-            if inspect.isclass(type):
-                elt = type().render(attributes)
+            if inspect.isclass(type_):
+                elt = type_().render(attributes)
             else:
-                elt = DOM.create_tag(type, attributes)
+                elt = DOM.create_tag(type_, attributes)
 
         for child in children:
             if child:
diff --git a/draftjs_exporter/entities.py b/draftjs_exporter/entities.py
index e0c15f8..2ee9d77 100644
--- a/draftjs_exporter/entities.py
+++ b/draftjs_exporter/entities.py
@@ -3,18 +3,18 @@ from __future__ import absolute_import, unicode_literals
 from draftjs_exporter.dom import DOM
 
 
-class Null():
+class Null:
     def render(self, props):
         return DOM.create_element()
 
 
-class Icon():
+class Icon:
     def render(self, props):
         href = 'icon-%s' % props.get('name', '')
         return DOM.create_element('svg', {'class': 'icon'}, DOM.create_element('use', {'xlink:href': href}))
 
 
-class Image():
+class Image:
     def render(self, props):
         data = props.get('data', {})
 
@@ -26,13 +26,13 @@ class Image():
         })
 
 
-class Link():
+class Link:
     attributes = ['url', 'rel', 'target', 'title']
 
     @staticmethod
     def is_valid_attribute(key):
         # TODO How much do we need to whitelist / blacklist attributes?
-        valid_data_attr = (key.startswith('data-') and key.replace('data-', '') and key.replace('data-', '').islower())
+        valid_data_attr = key.startswith('data-') and len(key) > 5 and key.islower()
         return key in Link.attributes or valid_data_attr
 
     def render(self, props):
@@ -48,11 +48,16 @@ class Link():
         return DOM.create_element('a', attributes)
 
 
-class Button():
+class Button:
     def render(self, props):
         data = props.get('data', {})
         href = data.get('href', '#')
         icon = data.get('icon', None)
         text = data.get('text', '')
 
-        return DOM.create_element('a', {'class': 'icon-text' if icon else None, 'href': href}, DOM.create_element(Icon, {'name': icon}) if icon else None, DOM.create_element('span', {'class': 'icon-text__text'}, text) if icon else text)
+        return DOM.create_element(
+            'a',
+            {'class': 'icon-text' if icon else None, 'href': href},
+            DOM.create_element(Icon, {'name': icon}) if icon else None,
+            DOM.create_element('span', {'class': 'icon-text__text'}, text) if icon else text
+        )
diff --git a/draftjs_exporter/entity_state.py b/draftjs_exporter/entity_state.py
index 2da83c6..b284a84 100644
--- a/draftjs_exporter/entity_state.py
+++ b/draftjs_exporter/entity_state.py
@@ -8,7 +8,7 @@ class EntityException(ExporterException):
     pass
 
 
-class EntityState():
+class EntityState:
     def __init__(self, root_element, entity_decorators, entity_map):
         self.entity_decorators = entity_decorators
         self.entity_map = entity_map
@@ -19,9 +19,9 @@ class EntityState():
         self.entity_stack = [(stack_start, {})]
 
     def apply(self, command):
-        if (command.name == 'start_entity'):
+        if command.name == 'start_entity':
             self.start_command(command)
-        elif (command.name == 'stop_entity'):
+        elif command.name == 'stop_entity':
             self.stop_command(command)
 
     def current_parent(self):
@@ -37,11 +37,11 @@ class EntityState():
         return details
 
     def get_entity_decorator(self, entity_details):
-        type = entity_details.get('type')
-        decorator = self.entity_decorators.get(type)
+        type_ = entity_details.get('type')
+        decorator = self.entity_decorators.get(type_)
 
         if decorator is None:
-            raise EntityException('Decorator "%s" does not exist in entity_decorators' % type)
+            raise EntityException('Decorator "%s" does not exist in entity_decorators' % type_)
 
         return decorator
 
@@ -52,7 +52,7 @@ class EntityState():
         new_element = decorator.render(entity_details)
         DOM.append_child(self.current_parent(), new_element)
 
-        self.entity_stack.append([new_element, entity_details])
+        self.entity_stack.append((new_element, entity_details))
 
     def stop_command(self, command):
         entity_details = self.get_entity_details(command)
diff --git a/draftjs_exporter/html.py b/draftjs_exporter/html.py
index c7be12d..b0cc16b 100644
--- a/draftjs_exporter/html.py
+++ b/draftjs_exporter/html.py
@@ -7,12 +7,15 @@ from draftjs_exporter.style_state import StyleState
 from draftjs_exporter.wrapper_state import WrapperState
 
 
-class HTML():
+class HTML:
     """
     Entry point of the exporter. Combines entity, wrapper and style state
     to generate the right HTML nodes.
     """
-    def __init__(self, config={}):
+    def __init__(self, config=None):
+        if config is None:
+            config = {}
+
         self.entity_decorators = config.get('entity_decorators', {})
         self.wrapper_state = WrapperState(config.get('block_map', BLOCK_MAP))
         self.style_state = StyleState(config.get('style_map', STYLE_MAP))
diff --git a/draftjs_exporter/style_state.py b/draftjs_exporter/style_state.py
index bb9ccdf..eed38d6 100644
--- a/draftjs_exporter/style_state.py
+++ b/draftjs_exporter/style_state.py
@@ -10,13 +10,13 @@ _first_cap_re = re.compile(r'(.)([A-Z][a-z]+)')
 _all_cap_re = re.compile('([a-z0-9])([A-Z])')
 
 
-def camelToDash(camelCasedStr):
-    sub2 = _first_cap_re.sub(r'\1-\2', camelCasedStr)
+def camel_to_dash(camel_cased_str):
+    sub2 = _first_cap_re.sub(r'\1-\2', camel_cased_str)
     dashed_case_str = _all_cap_re.sub(r'\1-\2', sub2).lower()
     return dashed_case_str.replace('--', '-')
 
 
-class StyleState():
+class StyleState:
     """
     Handles the creation of inline styles on elements.
     Receives inline_style commands, and generates the element's `style`
@@ -52,7 +52,7 @@ class StyleState():
             css_style = self.style_map.get(style, {})
             for prop in css_style.keys():
                 if prop != 'element':
-                    rules.append('{0}: {1};'.format(camelToDash(prop), css_style[prop]))
+                    rules.append('{0}: {1};'.format(camel_to_dash(prop), css_style[prop]))
 
         return ''.join(sorted(rules))
 
diff --git a/draftjs_exporter/wrapper_state.py b/draftjs_exporter/wrapper_state.py
index 8bec7e1..2879d99 100644
--- a/draftjs_exporter/wrapper_state.py
+++ b/draftjs_exporter/wrapper_state.py
@@ -8,7 +8,7 @@ class BlockException(ExporterException):
     pass
 
 
-class WrapperState():
+class WrapperState:
     """
     This class does the initial node building for the tree.
     It sets elements with the right tag, text content, and attributes.
@@ -25,19 +25,19 @@ class WrapperState():
         ]
 
     def element_for(self, block):
-        type = block.get('type', 'unstyled')
+        type_ = block.get('type', 'unstyled')
         depth = block.get('depth', 0)
-        block_options = self.get_block_options(type)
+        block_options = self.get_block_options(type_)
 
         # Make an element from the options specified in the block map.
         elt_options = self.map_element_options(block_options.get('element'))
         elt = DOM.create_element(elt_options[0], elt_options[1])
 
-        parent = self.parent_for(type, depth)
+        parent = self.parent_for(type_, depth)
         DOM.append_child(parent, elt)
 
         # At level 0, the element is added to the document.
-        if (depth == 0):
+        if depth == 0:
             DOM.append_child(self.document, parent)
 
         return elt
@@ -48,8 +48,8 @@ class WrapperState():
     def __str__(self):
         return '<WrapperState: %s>' % self.to_string()
 
-    def set_wrapper(self, options=[], depth=0):
-        if len(options) == 0:
+    def set_wrapper(self, options=None, depth=0):
+        if not options:
             element = DOM.create_document_fragment()
         else:
             element = DOM.create_element(options[0], options[1])
@@ -73,8 +73,8 @@ class WrapperState():
     def get_wrapper_options(self, depth=-1):
         return self.wrapper_stack[depth][2]
 
-    def parent_for(self, type, depth):
-        block_options = self.get_block_options(type)
+    def parent_for(self, type_, depth):
+        block_options = self.get_block_options(type_)
         wrapper_options = block_options.get('wrapper', None)
 
         if wrapper_options:
@@ -95,7 +95,7 @@ class WrapperState():
         ['ul']
         ['ul', {'className': 'bullet-list'}]
         """
-        if (isinstance(opts, list)):
+        if isinstance(opts, list):
             tag = opts[0]
             attributes = opts[1] if len(opts) > 1 else {}
         else:
@@ -104,11 +104,11 @@ class WrapperState():
 
         return [tag, attributes]
 
-    def get_block_options(self, type):
-        block_options = self.block_map.get(type)
+    def get_block_options(self, type_):
+        block_options = self.block_map.get(type_)
 
         if block_options is None:
-            raise BlockException('Block "%s" does not exist in block_map' % type)
+            raise BlockException('Block "%s" does not exist in block_map' % type_)
 
         return block_options
 

diff --git a/tests/test_constants.py b/tests/test_constants.py
index 8d4ad3d..1bf3a41 100644
--- a/tests/test_constants.py
+++ b/tests/test_constants.py
@@ -2,7 +2,21 @@ from __future__ import absolute_import, unicode_literals
 
 import unittest
 
-from draftjs_exporter.constants import BLOCK_TYPES, ENTITY_TYPES, INLINE_STYLES
+from draftjs_exporter.constants import Enum, BLOCK_TYPES, ENTITY_TYPES, INLINE_STYLES
+
+
+class EnumConstants(unittest.TestCase):
+    def test_enum_returns_the_key_if_valid(self):
+        foo_value = 'foo'
+        e = Enum(foo_value)
+
+        self.assertEqual(e.foo, foo_value)
+
+    def test_enum_raises_an_error_for_invalid_keys(self):
+        e = Enum('foo', 'bar')
+
+        with self.assertRaises(AttributeError):
+            e.invalid_key
 
 
 class TestConstants(unittest.TestCase):

Fix code relying on mutable default values
Pointed out by @loicteixeira, this happens a couple of times within the codebase.
tests/test_constants.py::EnumConstants::test_enum_raises_an_error_for_invalid_keys
tests/test_constants.py::EnumConstants::test_enum_returns_the_key_if_valid tests/test_constants.py::TestConstants::test_block_types tests/test_constants.py::TestConstants::test_entity_types tests/test_constants.py::TestConstants::test_inline_styles