Fix graph crash with partial conditions

Graph.rep() assumes that every callable has a `__name__` attribute.
However, callables like `functools.partial` and other classes with a
`__call__()` method have no `__name__`.  This patch modifies
`Graph.rep()` to first check whether the condition is a string and
return it, then try to return `f.__name__` (that is the current
behavior) and if that fails, then it calls `str()` on the argument.

`str()` should never fail and it is now the responsibility of the user
to return something meaningful from `__str__()`.

tests/test_graphing.py

@@ -75,6 +75,31 @@ def test_diagram(self):
         graph = m.get_graph(force_new=True, title=False)
         self.assertEqual("", graph.graph_attr['label'])
 
+    def test_anonymous_callable_conditions(self):
+        import functools
+        def check(result):
+            return result
+
+        class Check:
+            def __init__(self, result):
+                self.result = result
+            def __call__(self):
+                return self.result
+
+        m = self.machine_cls(states=self.states,
+                             transitions=self.transitions,
+                             initial='A',
+                             auto_transitions=False,
+                             show_conditions=True,
+                             title='a test')
+        m.add_state({'name': 'E'})
+        m.add_transition(trigger='fly', source='D', dest='E',
+                         conditions=Check(True))
+        m.add_transition(trigger='fly', source='D', dest='E',
+                         unless=functools.partial(check, False))
+        graph = m.get_graph()
+        self.assertIsNotNone(graph)
+
     def test_add_custom_state(self):
         m = self.machine_cls(states=self.states, transitions=self.transitions, initial='A', auto_transitions=False, title='a test')
         m.add_state('X')

transitions/extensions/diagrams.py

@@ -10,6 +10,7 @@
 
 import logging
 from functools import partial
+from six import string_types
 logger = logging.getLogger(__name__)
 logger.addHandler(logging.NullHandler())
 
@@ -117,7 +118,12 @@ def _is_auto_transition(self, event, label):
         return False
 
     def rep(self, f):
-        return f.__name__ if callable(f) else f
+        if isinstance(f, string_types):
+            return f
+        try:
+            return f.__name__
+        except AttributeError:
+            return str(f)
 
     def _transition_label(self, edge_label, tran):
         if self.machine.show_conditions and tran.conditions: