Make SkipTest give a better error. Remove duplicate code

theano/d3viz/formatting.py

@@ -14,25 +14,7 @@ from theano import gof
 from theano.compile.profilemode import ProfileMode
 from theano.compile import Function
 from theano.compile import builders
-
-pydot_imported = False
-try:
-    # pydot-ng is a fork of pydot that is better maintained
-    import pydot_ng as pd
-    if pd.find_graphviz():
-        pydot_imported = True
-except ImportError:
-    try:
-        # fall back on pydot if necessary
-        import pydot as pd
-        if hasattr(pd, 'find_graphviz'):
-            if pd.find_graphviz():
-                pydot_imported = True
-        else:
-            pd.Dot.create(pd.Dot())
-            pydot_imported = True
-    except ImportError:
-        pass  # tests should not fail on optional dependency
+from theano.printing import pd, pydot_imported, pydot_imported_msg
 
 
 class PyDotFormatter(object):
@@ -56,9 +38,8 @@ class PyDotFormatter(object):
     def __init__(self, compact=True):
         """Construct PyDotFormatter object."""
         if not pydot_imported:
-            raise ImportError('Failed to import pydot. You must install '
-                              'graphviz and either pydot or pydot-ng for '
-                              '`PyDotFormatter` to work.')
+            raise ImportError('Failed to import pydot. ' +
+                              pydot_imported_msg)
 
         self.compact = compact
         self.node_colors = {'input': 'limegreen',

theano/d3viz/tests/test_d3viz.py

@@ -11,9 +11,9 @@ import theano.d3viz as d3v
 from theano.d3viz.tests import models
 
 from nose.plugins.skip import SkipTest
-from theano.d3viz.formatting import pydot_imported
+from theano.d3viz.formatting import pydot_imported, pydot_imported_msg
 if not pydot_imported:
-    raise SkipTest('Missing requirements')
+    raise SkipTest('pydot not available: ' + pydot_imported_msg)
 
 
 class TestD3Viz(unittest.TestCase):

theano/d3viz/tests/test_formatting.py

@@ -8,9 +8,9 @@ from theano.d3viz.formatting import PyDotFormatter
 from theano.d3viz.tests import models
 
 from nose.plugins.skip import SkipTest
-from theano.d3viz.formatting import pydot_imported
+from theano.d3viz.formatting import pydot_imported, pydot_imported_msg
 if not pydot_imported:
-    raise SkipTest('Missing requirements')
+    raise SkipTest('pydot not available: ' + pydot_imported_msg)
 
 
 class TestPyDotFormatter(unittest.TestCase):

theano/printing.py

@@ -30,7 +30,7 @@ try:
     if pd.find_graphviz():
         pydot_imported = True
     else:
-        pydot_imported_msg = "pydot-ng can't find graphviz"
+        pydot_imported_msg = "pydot-ng can't find graphviz. Install graphviz."
 except ImportError:
     try:
         # fall back on pydot if necessary
@@ -45,7 +45,8 @@ except ImportError:
             pydot_imported = True
     except ImportError:
         # tests should not fail on optional dependency
-        pydot_imported_msg = "Install the python package pydot or pydot-ng."
+        pydot_imported_msg = ("Install the python package pydot or pydot-ng."
+                              " Install graphviz.")
 
 
 _logger = logging.getLogger("theano.printing")