Fix a bug in pydotprint when cond_highlight is set and there is no Cond Op in the graph.

theano/printing.py

 """Pretty-printing (pprint()), the 'Print' Op, debugprint() and pydotprint().
 They all allow different way to print a graph or the result of an Op in a graph(Print Op)
 """
-import sys, os, StringIO
 from copy import copy
+import logging
+import sys, os, StringIO
 
 import numpy
 
@@ -14,6 +15,12 @@ from theano.gof.python25 import any
 from theano.compile import Function, debugmode
 from theano.compile.profilemode import ProfileMode
 
+_logger=logging.getLogger("theano.tensor.basic")
+def _info(*msg):
+    _logger.info(' '.join(msg))
+def _warn(*msg):
+    _logger.warn(' '.join(msg))
+
 def debugprint(obj, depth=-1, print_type=False, file=None):
     """Print a computation graph to file
 
@@ -464,10 +471,15 @@ def pydotprint(fct, outfile=None,
         c1 = pd.Cluster('Left')
         c2 = pd.Cluster('Right')
         c3 = pd.Cluster('Middle')
+        cond = None
         for node in fct_env.toposort():
             if node.op.__class__.__name__=='Cond' and node.op.name == cond_highlight:
                 cond = node
+        if cond is None:
+            _warn("pydotprint: cond_highlight is set but there is no Cond node in the graph")
+            cond_highlight = None
 
+    if cond_highlight is not None:
         def recursive_pass(x,ls):
             if not x.owner:
                 return ls

theano/tests/test_printing.py

+"""
+This is a REALLY PARTIAL TEST.
+
+I did them to help debug stuff.
+
+"""
+
+
+import theano
+import theano.tensor as tensor
+
+
+def test_pydotprint_cond_highlight():
+    x = tensor.dvector()
+    f = theano.function([x], x*2)
+    f([1,2,3,4])
+
+    theano.printing.pydotprint(f, cond_highlight = True)