diff --git a/bonobo/__init__.py b/bonobo/__init__.py
index 628a96c..0d331c6 100644
--- a/bonobo/__init__.py
+++ b/bonobo/__init__.py
@@ -38,7 +38,7 @@ __all__ = [
     'Bag',
     'Graph',
     'NaiveStrategy',
-    'NotModified',
+    'NOT_MODIFIED',
     'ProcessPoolExecutorStrategy',
     'ThreadPoolExecutorStrategy',
     'head',
diff --git a/bonobo/core/bags.py b/bonobo/core/bags.py
index 8f86ab1..3ae71e8 100644
--- a/bonobo/core/bags.py
+++ b/bonobo/core/bags.py
@@ -6,7 +6,7 @@ from bonobo.util.tokens import Token
 
 _get_args = attrgetter('args')
 
-InheritInputFlag = Token('InheritInputFlag')
+INHERIT_INPUT = Token('InheritInput')
 
 
 class Bag:
@@ -37,8 +37,8 @@ class Bag:
     def flags(self):
         return self._flags
 
-    def apply(self, f, *args, **kwargs):
-        return f(*args, *self.args, **kwargs, **self.kwargs)
+    def apply(self, func, *args, **kwargs):
+        return func(*args, *self.args, **kwargs, **self.kwargs)
 
     def extend(self, *args, **kwargs):
         return type(self)(*args, _parent=self, **kwargs)
@@ -48,7 +48,7 @@ class Bag:
 
     @classmethod
     def inherit(cls, *args, **kwargs):
-        return cls(*args, _flags=(InheritInputFlag, ), **kwargs)
+        return cls(*args, _flags=(INHERIT_INPUT, ), **kwargs)
 
     def __repr__(self):
         return '<{} ({})>'.format(
diff --git a/bonobo/core/contexts.py b/bonobo/core/contexts.py
index a69ab51..d0935d4 100644
--- a/bonobo/core/contexts.py
+++ b/bonobo/core/contexts.py
@@ -3,12 +3,12 @@ from functools import partial
 from queue import Empty
 from time import sleep
 
-from bonobo.core.bags import Bag, InheritInputFlag
+from bonobo.core.bags import Bag, INHERIT_INPUT
 from bonobo.core.errors import InactiveReadableError
 from bonobo.core.inputs import Input
 from bonobo.core.stats import WithStatistics
 from bonobo.util.lifecycle import get_initializer, get_finalizer
-from bonobo.util.tokens import Begin, End, New, Running, Terminated, NotModified
+from bonobo.util.tokens import BEGIN, END, NEW, RUNNING, TERMINATED, NOT_MODIFIED
 
 
 class ExecutionContext:
@@ -23,8 +23,8 @@ class ExecutionContext:
                 component_context.outputs = [self[j].input for j in self.graph.outputs_of(i)]
             except KeyError:
                 continue
-            component_context.input.on_begin = partial(component_context.send, Begin, _control=True)
-            component_context.input.on_end = partial(component_context.send, End, _control=True)
+            component_context.input.on_begin = partial(component_context.send, BEGIN, _control=True)
+            component_context.input.on_end = partial(component_context.send, END, _control=True)
 
     def __getitem__(self, item):
         return self.components[item]
@@ -36,10 +36,10 @@ class ExecutionContext:
         yield from self.components
 
     def impulse(self):
-        for i in self.graph.outputs_of(Begin):
-            self[i].recv(Begin)
+        for i in self.graph.outputs_of(BEGIN):
+            self[i].recv(BEGIN)
             self[i].recv(Bag())
-            self[i].recv(End)
+            self[i].recv(END)
 
     @property
     def running(self):
@@ -85,13 +85,13 @@ def _iter(x):
 
 def _resolve(input_bag, output):
     # NotModified means to send the input unmodified to output.
-    if output is NotModified:
+    if output is NOT_MODIFIED:
         return input_bag
 
     # If it does not look like a bag, let's create one for easier manipulation
     if hasattr(output, 'apply'):
         # Already a bag? Check if we need to set parent.
-        if InheritInputFlag in output.flags:
+        if INHERIT_INPUT in output.flags:
             output.set_parent(input_bag)
     else:
         # Not a bag? Let's encapsulate it.
@@ -118,7 +118,7 @@ class ComponentExecutionContext(WithStatistics):
         self.component = component
         self.input = Input()
         self.outputs = []
-        self.state = New
+        self.state = NEW
         self.stats = {
             'in': 0,
             'out': 0,
@@ -198,10 +198,10 @@ class ComponentExecutionContext(WithStatistics):
                 self.send(_resolve(input_bag, output))
 
     def initialize(self):
-        assert self.state is New, ('A {} can only be run once, and thus is expected to be in {} state at '
-                                   'initialization time.').format(type(self).__name__, New)
+        assert self.state is NEW, ('A {} can only be run once, and thus is expected to be in {} state at '
+                                   'initialization time.').format(type(self).__name__, NEW)
 
-        self.state = Running
+        self.state = RUNNING
 
         try:
             get_initializer(self.component)(self)
@@ -209,10 +209,10 @@ class ComponentExecutionContext(WithStatistics):
             self.handle_error(e, traceback.format_exc())
 
     def finalize(self):
-        assert self.state is Running, ('A {} must be in {} state at finalization time.').format(
-            type(self).__name__, Running)
+        assert self.state is RUNNING, ('A {} must be in {} state at finalization time.').format(
+            type(self).__name__, RUNNING)
 
-        self.state = Terminated
+        self.state = TERMINATED
         try:
             get_finalizer(self.component)(self)
         except Exception as e:
diff --git a/bonobo/core/graphs.py b/bonobo/core/graphs.py
index df79777..e9ffeb5 100644
--- a/bonobo/core/graphs.py
+++ b/bonobo/core/graphs.py
@@ -1,4 +1,4 @@
-from bonobo.util.tokens import Begin
+from bonobo.util.tokens import BEGIN
 
 
 class Graph:
@@ -8,7 +8,7 @@ class Graph:
 
     def __init__(self):
         self.components = []
-        self.graph = {Begin: set()}
+        self.graph = {BEGIN: set()}
 
     def outputs_of(self, idx, create=False):
         if create and not idx in self.graph:
@@ -20,7 +20,7 @@ class Graph:
         self.components.append(c)
         return i
 
-    def add_chain(self, *components, _input=Begin):
+    def add_chain(self, *components, _input=BEGIN):
         for component in components:
             _next = self.add_component(component)
             self.outputs_of(_input, create=True).add(_next)
diff --git a/bonobo/core/inputs.py b/bonobo/core/inputs.py
index 6b01c2c..1680e18 100644
--- a/bonobo/core/inputs.py
+++ b/bonobo/core/inputs.py
@@ -19,7 +19,7 @@ from queue import Queue
 
 from bonobo.core.errors import AbstractError, InactiveWritableError, InactiveReadableError
 from bonobo.util import noop
-from bonobo.util.tokens import Begin, End
+from bonobo.util.tokens import BEGIN, END
 
 BUFFER_SIZE = 8192
 
@@ -53,7 +53,7 @@ class Input(Queue, Readable, Writable):
 
     def put(self, data, block=True, timeout=None):
         # Begin token is a metadata to raise the input runlevel.
-        if data == Begin:
+        if data == BEGIN:
             self._runlevel += 1
             self._writable_runlevel += 1
 
@@ -66,7 +66,7 @@ class Input(Queue, Readable, Writable):
         if self._writable_runlevel < 1:
             raise InactiveWritableError('Cannot put() on an inactive {}.'.format(Writable.__name__))
 
-        if data == End:
+        if data == END:
             self._writable_runlevel -= 1
 
         return Queue.put(self, data, block, timeout)
@@ -77,7 +77,7 @@ class Input(Queue, Readable, Writable):
 
         data = Queue.get(self, block, timeout)
 
-        if data == End:
+        if data == END:
             self._runlevel -= 1
 
             # callback
@@ -92,7 +92,7 @@ class Input(Queue, Readable, Writable):
 
     def empty(self):
         self.mutex.acquire()
-        while self._qsize() and self.queue[0] == End:
+        while self._qsize() and self.queue[0] == END:
             self._runlevel -= 1
             Queue._get(self)
         self.mutex.release()
diff --git a/bonobo/util/__init__.py b/bonobo/util/__init__.py
index 38e1f39..d75720c 100644
--- a/bonobo/util/__init__.py
+++ b/bonobo/util/__init__.py
@@ -3,10 +3,10 @@
 import functools
 import pprint
 
-from .tokens import NotModified
+from .tokens import NOT_MODIFIED
 
 __all__ = [
-    'NotModified',
+    'NOT_MODIFIED',
     'head',
     'log',
     'noop',
diff --git a/bonobo/util/tokens.py b/bonobo/util/tokens.py
index e8a9164..98c0fae 100644
--- a/bonobo/util/tokens.py
+++ b/bonobo/util/tokens.py
@@ -8,11 +8,11 @@ class Token:
         return '<{}>'.format(self.__name__)
 
 
-Begin = Token('Begin')
-End = Token('End')
+BEGIN = Token('Begin')
+END = Token('End')
 
-New = Token('New')
-Running = Token('Running')
-Terminated = Token('Terminated')
+NEW = Token('New')
+RUNNING = Token('Running')
+TERMINATED = Token('Terminated')
 
-NotModified = Token('NotModified')
+NOT_MODIFIED = Token('NotModified')
diff --git a/tests/core/test_bags.py b/tests/core/test_bags.py
index 87bc2b0..5998381 100644
--- a/tests/core/test_bags.py
+++ b/tests/core/test_bags.py
@@ -1,7 +1,7 @@
 from mock import Mock
 
 from bonobo import Bag
-from bonobo.core.bags import InheritInputFlag
+from bonobo.core.bags import INHERIT_INPUT
 
 args = (
     'foo',
@@ -42,7 +42,7 @@ def test_inherit():
         'a',
         'b', )
     assert bag2.kwargs == {'a': 1, 'b': 2}
-    assert InheritInputFlag in bag2.flags
+    assert INHERIT_INPUT in bag2.flags
 
     assert bag3.args == (
         'a',
diff --git a/tests/core/test_graphs.py b/tests/core/test_graphs.py
index e9f67c7..47a7dbd 100644
--- a/tests/core/test_graphs.py
+++ b/tests/core/test_graphs.py
@@ -1,7 +1,7 @@
 import pytest
 
 from bonobo.core.graphs import Graph
-from bonobo.util.tokens import Begin
+from bonobo.util.tokens import BEGIN
 
 identity = lambda x: x
 
@@ -10,7 +10,7 @@ def test_graph_outputs_of():
     g = Graph()
 
     # default graph only node
-    assert len(g.outputs_of(Begin)) == 0
+    assert len(g.outputs_of(BEGIN)) == 0
 
     # unexisting node
     with pytest.raises(KeyError):
@@ -40,4 +40,4 @@ def test_graph_add_chain():
 
     g.add_chain(identity, identity, identity)
     assert len(g.components) == 3
-    assert len(g.outputs_of(Begin)) == 1
+    assert len(g.outputs_of(BEGIN)) == 1
diff --git a/tests/core/test_inputs.py b/tests/core/test_inputs.py
index 4a591d3..6b421e3 100644
--- a/tests/core/test_inputs.py
+++ b/tests/core/test_inputs.py
@@ -20,7 +20,7 @@ import pytest
 
 from bonobo.core.errors import InactiveWritableError, InactiveReadableError
 from bonobo.core.inputs import Input
-from bonobo.util.tokens import Begin, End
+from bonobo.util.tokens import BEGIN, END
 
 
 def test_input_runlevels():
@@ -32,15 +32,15 @@ def test_input_runlevels():
         q.put('hello, unborn queue.')
 
     # Begin
-    q.put(Begin)
+    q.put(BEGIN)
     assert q.alive and q._runlevel == 1
     q.put('foo')
 
     # Second Begin
-    q.put(Begin)
+    q.put(BEGIN)
     assert q.alive and q._runlevel == 2
     q.put('bar')
-    q.put(End)
+    q.put(END)
 
     # FIFO
     assert q.get() == 'foo'
@@ -56,7 +56,7 @@ def test_input_runlevels():
     q.put('baz')
 
     # Now kill the queue...
-    q.put(End)
+    q.put(END)
     with pytest.raises(InactiveWritableError):
         q.put('foo')