diff --git a/.gitignore b/.gitignore
index a88bd7b..d48b40b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -37,6 +37,7 @@
 /examples/private
 /htmlcov/
 /sdist/
+/tags
 celerybeat-schedule
 parts/
 pip-delete-this-directory.txt
diff --git a/bonobo/config/configurables.py b/bonobo/config/configurables.py
index c1486ee..64b4adc 100644
--- a/bonobo/config/configurables.py
+++ b/bonobo/config/configurables.py
@@ -85,3 +85,8 @@ class Configurable(metaclass=ConfigurableMeta):
         # set option values.
         for name, value in kwargs.items():
             setattr(self, name, value)
+
+    def __call__(self, *args, **kwargs):
+        """ You can implement a configurable callable behaviour by implemenenting the call(...) method. Of course, it is also backward compatible with legacy __call__ override.
+        """
+        return self.call(*args, **kwargs)
diff --git a/bonobo/examples/__init__.py b/bonobo/examples/__init__.py
index cf3d84d..49b1544 100644
--- a/bonobo/examples/__init__.py
+++ b/bonobo/examples/__init__.py
@@ -5,9 +5,19 @@ def require(package, requirement=None):
         return __import__(package)
     except ImportError:
         from colorama import Fore, Style
-        print(Fore.YELLOW, 'This example requires the {!r} package. Install it using:'.format(requirement),
-              Style.RESET_ALL, sep='')
+        print(
+            Fore.YELLOW,
+            'This example requires the {!r} package. Install it using:'.
+            format(requirement),
+            Style.RESET_ALL,
+            sep=''
+        )
         print()
-        print(Fore.YELLOW, '  $ pip install {!s}'.format(requirement), Style.RESET_ALL, sep='')
+        print(
+            Fore.YELLOW,
+            '  $ pip install {!s}'.format(requirement),
+            Style.RESET_ALL,
+            sep=''
+        )
         print()
-        raise
\ No newline at end of file
+        raise
diff --git a/bonobo/execution/base.py b/bonobo/execution/base.py
index e1b9bb0..6ca22f2 100644
--- a/bonobo/execution/base.py
+++ b/bonobo/execution/base.py
@@ -87,7 +87,6 @@ class LoopingExecutionContext(Wrapper):
         finally:
             self._stopped = True
 
-
     def handle_error(self, exc, trace):
         return print_error(exc, trace, context=self.wrapped)
 
diff --git a/bonobo/execution/graph.py b/bonobo/execution/graph.py
index 2e55492..1f2671a 100644
--- a/bonobo/execution/graph.py
+++ b/bonobo/execution/graph.py
@@ -21,7 +21,7 @@ class GraphExecutionContext:
 
     def __init__(self, graph, plugins=None, services=None):
         self.graph = graph
-        self.nodes = [NodeExecutionContext(node, parent=self) for node in self.graph.nodes]
+        self.nodes = [NodeExecutionContext(node, parent=self) for node in self.graph]
         self.plugins = [PluginExecutionContext(plugin, parent=self) for plugin in plugins or ()]
         self.services = Container(services) if services else Container()
 
@@ -65,4 +65,4 @@ class GraphExecutionContext:
     def stop(self):
         # todo use strategy
         for node in self.nodes:
-            node.stop()
\ No newline at end of file
+            node.stop()
diff --git a/bonobo/ext/console/plugin.py b/bonobo/ext/console/plugin.py
index d76b3af..8884a73 100644
--- a/bonobo/ext/console/plugin.py
+++ b/bonobo/ext/console/plugin.py
@@ -73,19 +73,19 @@ class ConsoleOutputPlugin(Plugin):
     def write(context, prefix='', rewind=True, append=None, debug=False, profile=False):
         t_cnt = len(context)
 
-        for i, node in enumerate(context):
+        for i in context.graph.topologically_sorted_indexes:
+            node = context[i]
             if node.alive:
                 _line = ''.join(
                     (
-                        Fore.BLACK, '({})'.format(i + 1), Style.RESET_ALL, ' ', Style.BRIGHT, '+', Style.RESET_ALL, ' ',
-                        node.name, ' ', node.get_statistics_as_string(debug=debug,
-                                                                                profile=profile), Style.RESET_ALL, ' ',
+                        ' ', Style.BRIGHT, '+', Style.RESET_ALL, ' ', node.name, '(', str(i), ') ',
+                        node.get_statistics_as_string(debug=debug, profile=profile), Style.RESET_ALL, ' ',
                     )
                 )
             else:
                 _line = ''.join(
                     (
-                        Fore.BLACK, '({})'.format(i + 1), ' - ', node.name, ' ',
+                        ' ', Fore.BLACK, '-', ' ', node.name, '(', str(i), ') ',
                         node.get_statistics_as_string(debug=debug, profile=profile), Style.RESET_ALL, ' ',
                     )
                 )
diff --git a/bonobo/io/csv.py b/bonobo/io/csv.py
index 30ad3a4..647925b 100644
--- a/bonobo/io/csv.py
+++ b/bonobo/io/csv.py
@@ -55,7 +55,7 @@ class CsvReader(CsvHandler, FileReader):
 
         for row in reader:
             if len(row) != field_count:
-                raise ValueError('Got a line with %d fields, expecting %d.' % (len(row), field_count,))
+                raise ValueError('Got a line with %d fields, expecting %d.' % (len(row), field_count, ))
 
             yield dict(zip(headers.value, row))
 
@@ -74,5 +74,3 @@ class CsvWriter(CsvHandler, FileWriter):
         writer.writerow(row[header] for header in headers.value)
         lineno.value += 1
         return NOT_MODIFIED
-
-
diff --git a/bonobo/structs/bags.py b/bonobo/structs/bags.py
index e1fc442..3414d00 100644
--- a/bonobo/structs/bags.py
+++ b/bonobo/structs/bags.py
@@ -43,7 +43,7 @@ class Bag:
     def args(self):
         if self._parent is None:
             return self._args
-        return (*self._parent.args, *self._args,)
+        return (*self._parent.args, *self._args, )
 
     @property
     def kwargs(self):
@@ -85,7 +85,7 @@ class Bag:
 
     @classmethod
     def inherit(cls, *args, **kwargs):
-        return cls(*args, _flags=(INHERIT_INPUT,), **kwargs)
+        return cls(*args, _flags=(INHERIT_INPUT, ), **kwargs)
 
     def __eq__(self, other):
         return isinstance(other, Bag) and other.args == self.args and other.kwargs == self.kwargs
@@ -93,7 +93,7 @@ class Bag:
     def __repr__(self):
         return '<{} ({})>'.format(
             type(self).__name__, ', '.
-                join(itertools.chain(
+            join(itertools.chain(
                 map(repr, self.args),
                 ('{}={}'.format(k, repr(v)) for k, v in self.kwargs.items()),
             ))
diff --git a/bonobo/structs/graphs.py b/bonobo/structs/graphs.py
index 8fcc0e6..ccafb6b 100644
--- a/bonobo/structs/graphs.py
+++ b/bonobo/structs/graphs.py
@@ -3,35 +3,115 @@ from bonobo.constants import BEGIN
 
 class Graph:
     """
-    Represents a coherent directed acyclic graph of components.
+    Represents a directed graph of nodes.
     """
 
     def __init__(self, *chain):
+        self.edges = {BEGIN: set()}
+        self.named = {}
         self.nodes = []
-        self.graph = {BEGIN: set()}
         self.add_chain(*chain)
 
+    def __iter__(self):
+        yield from self.nodes
+
+    def __len__(self):
+        """ Node count.
+        """
+        return len(self.nodes)
+
+    def __getitem__(self, key):
+        return self.nodes[key]
+
     def outputs_of(self, idx, create=False):
-        if create and not idx in self.graph:
-            self.graph[idx] = set()
-        return self.graph[idx]
+        """ Get a set of the outputs for a given node index.
+        """
+        if create and not idx in self.edges:
+            self.edges[idx] = set()
+        return self.edges[idx]
 
     def add_node(self, c):
-        i = len(self.nodes)
+        """ Add a node without connections in this graph and returns its index.
+        """
+        idx = len(self.nodes)
+        self.edges[idx] = set()
         self.nodes.append(c)
-        return i
+        return idx
 
-    def add_chain(self, *nodes, _input=BEGIN, _output=None):
-        for node in nodes:
-            _next = self.add_node(node)
-            self.outputs_of(_input, create=True).add(_next)
-            _input = _next
-        if _output:
-            if not _output in self.nodes:
-                raise ValueError('Output not found.')
-            self.outputs_of(_input, create=True).add(self.nodes.index(_output))
+    def add_chain(self, *nodes, _input=BEGIN, _output=None, _name=None):
+        """ Add a chain in this graph.
+        """
+        if len(nodes):
+            _input = self._resolve_index(_input)
+            _output = self._resolve_index(_output)
+
+            for i, node in enumerate(nodes):
+                _next = self.add_node(node)
+                if not i and _name:
+                    if _name in self.named:
+                        raise KeyError('Duplicate name {!r} in graph.'.format(_name))
+                    self.named[_name] = _next
+                self.outputs_of(_input, create=True).add(_next)
+                _input = _next
+
+            if _output is not None:
+                self.outputs_of(_input, create=True).add(_output)
+
+            if hasattr(self, '_topologcally_sorted_indexes_cache'):
+                del self._topologcally_sorted_indexes_cache
 
         return self
 
-    def __len__(self):
-        return len(self.nodes)
+    @property
+    def topologically_sorted_indexes(self):
+        """Iterate in topological order, based on networkx's topological_sort() function.
+        """
+        try:
+            return self._topologcally_sorted_indexes_cache
+        except AttributeError:
+            seen = set()
+            order = []
+            explored = set()
+
+            for i in self.edges:
+                if i in explored:
+                    continue
+                fringe = [i]
+                while fringe:
+                    w = fringe[-1]  # depth first search
+                    if w in explored:  # already looked down this branch
+                        fringe.pop()
+                        continue
+                    seen.add(w)  # mark as seen
+                    # Check successors for cycles and for new nodes
+                    new_nodes = []
+                    for n in self.outputs_of(w):
+                        if n not in explored:
+                            if n in seen:  # CYCLE !!
+                                raise RuntimeError("Graph contains a cycle.")
+                            new_nodes.append(n)
+                    if new_nodes:  # Add new_nodes to fringe
+                        fringe.extend(new_nodes)
+                    else:  # No new nodes so w is fully explored
+                        explored.add(w)
+                        order.append(w)
+                        fringe.pop()  # done considering this node
+            self._topologcally_sorted_indexes_cache = tuple(filter(lambda i: type(i) is int, reversed(order)))
+            return self._topologcally_sorted_indexes_cache
+
+    def _resolve_index(self, mixed):
+        """ Find the index based on various strategies for a node, probably an input or output of chain. Supported inputs are indexes, node values or names.
+        """
+        if mixed is None:
+            return None
+
+        if type(mixed) is int or mixed in self.edges:
+            return mixed
+
+        if isinstance(mixed, str) and mixed in self.named:
+            return self.named[mixed]
+
+        if mixed in self.nodes:
+            return self.nodes.index(mixed)
+
+        raise ValueError('Cannot find node matching {!r}.'.format(mixed))
diff --git a/bonobo/util/objects.py b/bonobo/util/objects.py
index 8b5db00..1e0015a 100644
--- a/bonobo/util/objects.py
+++ b/bonobo/util/objects.py
@@ -200,6 +200,9 @@ class ValueHolder:
     def __invert__(self):
         return ~self.value
 
+    def __len__(self):
+        return len(self.value)
+
 
 def get_attribute_or_create(obj, attr, default):
     try:
@@ -207,4 +210,3 @@ def get_attribute_or_create(obj, attr, default):
     except AttributeError:
         setattr(obj, attr, default)
         return getattr(obj, attr)
-
diff --git a/bonobo/util/python.py b/bonobo/util/python.py
new file mode 100644
index 0000000..a496e19
--- /dev/null
+++ b/bonobo/util/python.py
@@ -0,0 +1,22 @@
+import inspect
+import os
+import runpy
+
+
+class _RequiredModule:
+    def __init__(self, dct):
+        self.__dict__ = dct
+
+
+class _RequiredModulesRegistry(dict):
+    def require(self, name):
+        if name not in self:
+            bits = name.split('.')
+            pathname = os.path.join(os.getcwd(), os.path.dirname(inspect.getfile(inspect.stack()[1][0])))
+            filename = os.path.join(pathname, *bits[:-1], bits[-1] + '.py')
+            self[name] = _RequiredModule(runpy.run_path(filename, run_name=name))
+        return self[name]
+
+
+registry = _RequiredModulesRegistry()
+require = registry.require
diff --git a/setup.py b/setup.py
index 4cd8d82..844240a 100644
--- a/setup.py
+++ b/setup.py
@@ -36,44 +36,41 @@ else:
 
 setup(
     name='bonobo',
-    description=
-    ('Bonobo, a simple, modern and atomic extract-transform-load toolkit for '
-     'python 3.5+.'),
+    description=('Bonobo, a simple, modern and atomic extract-transform-load toolkit for '
+                 'python 3.5+.'),
     license='Apache License, Version 2.0',
     install_requires=[
-        'colorama >=0.3,<1.0', 'fs >=2.0,<3.0', 'psutil >=5.2,<6.0',
-        'requests >=2.0,<3.0', 'stevedore >=1.21,<2.0'
+        'colorama >=0.3,<1.0', 'fs >=2.0,<3.0', 'psutil >=5.2,<6.0', 'requests >=2.0,<3.0', 'stevedore >=1.21,<2.0'
     ],
     version=version,
     long_description=long_description,
     classifiers=classifiers,
     packages=find_packages(exclude=['ez_setup', 'example', 'test']),
     include_package_data=True,
-    data_files=[('share/jupyter/nbextensions/bonobo-jupyter', [
-        'bonobo/ext/jupyter/static/extension.js',
-        'bonobo/ext/jupyter/static/index.js',
-        'bonobo/ext/jupyter/static/index.js.map'
-    ])],
+    data_files=[
+        (
+            'share/jupyter/nbextensions/bonobo-jupyter', [
+                'bonobo/ext/jupyter/static/extension.js', 'bonobo/ext/jupyter/static/index.js',
+                'bonobo/ext/jupyter/static/index.js.map'
+            ]
+        )
+    ],
     extras_require={
         'dev': [
-            'coverage >=4,<5', 'pylint >=1,<2', 'pytest >=3,<4',
-            'pytest-cov >=2,<3', 'pytest-timeout >=1,<2', 'sphinx',
+            'coverage >=4,<5', 'pylint >=1,<2', 'pytest >=3,<4', 'pytest-cov >=2,<3', 'pytest-timeout >=1,<2', 'sphinx',
             'sphinx_rtd_theme', 'yapf'
         ],
         'jupyter': ['jupyter >=1.0,<1.1', 'ipywidgets >=6.0.0.beta5']
     },
     entry_points={
         'bonobo.commands': [
-            'init = bonobo.commands.init:register',
-            'run = bonobo.commands.run:register',
+            'init = bonobo.commands.init:register', 'run = bonobo.commands.run:register',
             'version = bonobo.commands.version:register'
         ],
         'console_scripts': ['bonobo = bonobo.commands:entrypoint'],
-        'edgy.project.features':
-        ['bonobo = '
-         'bonobo.ext.edgy.project.feature:BonoboFeature']
+        'edgy.project.features': ['bonobo = '
+                                  'bonobo.ext.edgy.project.feature:BonoboFeature']
     },
     url='https://www.bonobo-project.org/',
-    download_url=
-    'https://github.com/python-bonobo/bonobo/tarball/{version}'.format(
-        version=version), )
+    download_url='https://github.com/python-bonobo/bonobo/tarball/{version}'.format(version=version),
+)
diff --git a/tests/structs/test_bags.py b/tests/structs/test_bags.py
index 1d44026..fbb4f5b 100644
--- a/tests/structs/test_bags.py
+++ b/tests/structs/test_bags.py
@@ -5,7 +5,7 @@ from bonobo import Bag
 from bonobo.constants import INHERIT_INPUT
 from bonobo.structs import Token
 
-args = ('foo', 'bar',)
+args = ('foo', 'bar', )
 kwargs = dict(acme='corp')
 
 
@@ -34,29 +34,29 @@ def test_inherit():
     bag3 = bag.extend('c', c=3)
     bag4 = Bag('d', d=4)
 
-    assert bag.args == ('a',)
+    assert bag.args == ('a', )
     assert bag.kwargs == {'a': 1}
     assert bag.flags is ()
 
-    assert bag2.args == ('a', 'b',)
+    assert bag2.args == ('a', 'b', )
     assert bag2.kwargs == {'a': 1, 'b': 2}
     assert INHERIT_INPUT in bag2.flags
 
-    assert bag3.args == ('a', 'c',)
+    assert bag3.args == ('a', 'c', )
     assert bag3.kwargs == {'a': 1, 'c': 3}
     assert bag3.flags is ()
 
-    assert bag4.args == ('d',)
+    assert bag4.args == ('d', )
     assert bag4.kwargs == {'d': 4}
     assert bag4.flags is ()
 
     bag4.set_parent(bag)
-    assert bag4.args == ('a', 'd',)
+    assert bag4.args == ('a', 'd', )
     assert bag4.kwargs == {'a': 1, 'd': 4}
     assert bag4.flags is ()
 
     bag4.set_parent(bag3)
-    assert bag4.args == ('a', 'c', 'd',)
+    assert bag4.args == ('a', 'c', 'd', )
     assert bag4.kwargs == {'a': 1, 'c': 3, 'd': 4}
     assert bag4.flags is ()
 
diff --git a/tests/structs/test_graphs.py b/tests/structs/test_graphs.py
index c1c29c2..3afeaee 100644
--- a/tests/structs/test_graphs.py
+++ b/tests/structs/test_graphs.py
@@ -1,5 +1,7 @@
 import pytest
 
+from unittest.mock import sentinel
+
 from bonobo.constants import BEGIN
 from bonobo.structs import Graph
 
@@ -41,3 +43,30 @@ def test_graph_add_chain():
     g.add_chain(identity, identity, identity)
     assert len(g.nodes) == 3
     assert len(g.outputs_of(BEGIN)) == 1
+
+
+def test_graph_topological_sort():
+    g = Graph()
+
+    g.add_chain(
+        sentinel.a1,
+        sentinel.a2,
+        sentinel.a3,
+        _input=None,
+        _output=None,
+    )
+
+    assert g.topologically_sorted_indexes == (0, 1, 2)
+    assert g[0] == sentinel.a1
+    assert g[1] == sentinel.a2
+    assert g[2] == sentinel.a3
+
+    g.add_chain(
+        sentinel.b1,
+        sentinel.b2,
+        _output=sentinel.a2,
+    )
+
+    assert g.topologically_sorted_indexes == (0, 3, 4, 1, 2)
+    assert g[3] == sentinel.b1
+    assert g[4] == sentinel.b2
diff --git a/tests/util/requireable/dummy.py b/tests/util/requireable/dummy.py
new file mode 100644
index 0000000..1ce8ef1
--- /dev/null
+++ b/tests/util/requireable/dummy.py
@@ -0,0 +1 @@
+foo = 'bar'
diff --git a/tests/util/test_python.py b/tests/util/test_python.py
new file mode 100644
index 0000000..6b1b591
--- /dev/null
+++ b/tests/util/test_python.py
@@ -0,0 +1,6 @@
+from bonobo.util.python import require
+
+
+def test_require():
+    dummy = require('requireable.dummy')
+    assert dummy.foo == 'bar'