fixed several errors

Author: oesteban

nipype/pipeline/engine/nodes.py

@@ -376,7 +376,7 @@ def connect(self, *args, **kwargs):
                         # handles the case that source is specified
                         # with a function
                         sourcename = source[0]
-                    elif isinstance(source, six.string_types):
+                    elif isinstance(source, string_types):
                         sourcename = source
                     else:
                         raise Exception(('Unknown source specification in '
@@ -397,7 +397,7 @@ def connect(self, *args, **kwargs):
         # turn functions into strings
         for srcnode, destnode, connects in connection_list:
             for idx, (src, dest) in enumerate(connects):
-                if isinstance(src, tuple) and not isinstance(src[1], six.string_types):
+                if isinstance(src, tuple) and not isinstance(src[1], string_types):
                     function_source = getsource(src[1])
                     connects[idx] = ((src[0], function_source, src[2:]), dest)
 
@@ -918,7 +918,7 @@ def _set_input(self, object, name, newvalue):
 
     def _set_node_input(self, node, param, source, sourceinfo):
         """Set inputs of a node given the edge connection"""
-        if isinstance(sourceinfo, six.string_types):
+        if isinstance(sourceinfo, string_types):
             val = source.get_output(sourceinfo)
         elif isinstance(sourceinfo, tuple):
             if callable(sourceinfo[1]):