Make it Compatible with Python3

Exception, print Syntax is not compatible with python3, this patch
fixes it. Following changes are done:

- except Exception, e  => except Exception as e
- raise Error, "MSG" => raise Error("MSG")
- print "MSG" => print("MSG")

pydot/__init__.py

@@ -29,8 +29,8 @@
 import copy
 try:
     import dot_parser
-except Exception, e:
-    print "Couldn't import dot_parser, loading of dot files will not be possible."
+except Exception as e:
+    print("Couldn't import dot_parser, loading of dot files will not be possible.")
 
 GRAPH_ATTRIBUTES = set( ['Damping', 'K', 'URL', 'aspect', 'bb', 'bgcolor',
     'center', 'charset', 'clusterrank', 'colorscheme', 'comment', 'compound',
@@ -90,7 +90,7 @@
 #
 class frozendict(dict):
     def _blocked_attribute(obj):
-        raise AttributeError, "A frozendict cannot be modified."
+        raise AttributeError("A frozendict cannot be modified.")
     _blocked_attribute = property(_blocked_attribute)
 
     __delitem__ = __setitem__ = clear = _blocked_attribute
@@ -501,10 +501,10 @@ def RegQueryValueEx( hkey, valuename ):
                         path = os.path.join(path, "bin")
                         progs = __find_executables(path)
                         if progs is not None :
-                            #print "Used Windows registry"
+                            #print("Used Windows registry")
                             return progs
 
-                except Exception, excp:
+                except Exception as excp:
                     #raise excp
                     pass
                 else:
@@ -519,7 +519,7 @@ def RegQueryValueEx( hkey, valuename ):
         for path in os.environ['PATH'].split(os.pathsep):
             progs = __find_executables(path)
             if progs is not None :
-                #print "Used path"
+                #print("Used path")
                 return progs
 
     # Method 3 (Windows only)
@@ -546,7 +546,7 @@ def RegQueryValueEx( hkey, valuename ):
 
         if progs is not None :
 
-            #print "Used default install location"
+            #print("Used default install location")
             return progs
 
 
@@ -558,7 +558,7 @@ def RegQueryValueEx( hkey, valuename ):
 
         progs = __find_executables(path)
         if progs is not None :
-            #print "Used path"
+            #print("Used path")
             return progs
 
     # Failed to find GraphViz
@@ -923,7 +923,7 @@ def __eq__(self, edge):
         """
 
         if not isinstance(edge, Edge):
-            raise Error, "Can't compare and edge to a non-edge object."
+            raise Error("Can't compare and edge to a non-edge object.")
 
         if self.get_parent_graph().get_top_graph_type() == 'graph':
 
@@ -1073,7 +1073,7 @@ def __init__(self, graph_name='G', obj_dict=None, graph_type='digraph', strict=F
             self.obj_dict['attributes'] = dict(attrs)
 
             if graph_type not in ['graph', 'digraph']:
-                raise Error, 'Invalid type "%s". Accepted graph types are: graph, digraph, subgraph' % graph_type
+                raise Error('Invalid type "%s". Accepted graph types are: graph, digraph, subgraph' % graph_type)
 
 
             self.obj_dict['name'] = quote_if_necessary(graph_name)
@@ -2020,7 +2020,7 @@ def create(self, prog=None, format='ps'):
                 'Program terminated with status: %d. stderr follows: %s' % (
                     status, stderr_output) )
         elif stderr_output:
-            print stderr_output
+            print(stderr_output)
 
         # For each of the image files...
         #

pydot/dot_parser.py

@@ -113,7 +113,7 @@ def push_top_graph_stmt(str, loc, toks):
             add_elements(g, element)
 
         else:
-            raise ValueError, "Unknown element statement: %r " % element
+            raise ValueError("Unknown element statement: %r " % element)
 
 
     for g in top_graphs:
@@ -220,14 +220,14 @@ def add_elements(g, toks, defaults_graph=None, defaults_node=None, defaults_edge
                 defaults_edge.update(element.attrs)
 
             else:
-                raise ValueError, "Unknown DefaultStatement: %s " % element.default_type
+                raise ValueError("Unknown DefaultStatement: %s " % element.default_type)
 
         elif isinstance(element, P_AttrList):
 
             g.obj_dict['attributes'].update(element.attrs)
 
         else:
-            raise ValueError, "Unknown element statement: %r" % element
+            raise ValueError("Unknown element statement: %r" % element)
 
 
 def push_graph_stmt(str, loc, toks):            
@@ -269,7 +269,7 @@ def push_default_stmt(str, loc, toks):
     if default_type in ['graph', 'node', 'edge']:
         return DefaultStatement(default_type, attrs)
     else:
-        raise ValueError, "Unknown default statement: %r " % toks
+        raise ValueError("Unknown default statement: %r " % toks)
 
 
 def push_attr_list(str, loc, toks):
@@ -525,9 +525,9 @@ def parse_dot_data(data):
         else:
             return [g for g in tokens]
 
-    except ParseException, err:
+    except ParseException as err:
 
-        print err.line
-        print " "*(err.column-1) + "^"
-        print err
+        print(err.line)
+        print(" "*(err.column-1) + "^")
+        print(err)
         return None