Fixed bug in drawing of graphviz edges from interaction nodes by repl…

…acing colons in node names with ampersands. (#3414)

Ampersands are a safe replacement: they will not cause accidental node name collisions because they aren't allowed in python names (nor, by extension, in patsy formulas).

pymc3/model_graph.py

@@ -108,7 +108,7 @@ def _make_node(self, var_name, graph):
             distribution = 'Deterministic'
             attrs['shape'] = 'box'
 
-        graph.node(var_name,
+        graph.node(var_name.replace(':', '&'),
                 '{var_name} ~ {distribution}'.format(var_name=var_name, distribution=distribution),
                 **attrs)
 
@@ -167,7 +167,7 @@ def make_graph(self):
 
         for key, values in self.make_compute_graph().items():
             for value in values:
-                graph.edge(value, key)
+                graph.edge(value.replace(':', '&'), key.replace(':', '&'))
         return graph