Rename Extension to FilenameExtension

IPython/nbconvert/exporters/__init__.py

@@ -8,4 +8,4 from .notebook import NotebookExporter
 from .pdf import PDFExporter
 from .python import PythonExporter
 from .rst import RSTExporter
-from .exporter import Exporter, Extension
+from .exporter import Exporter, FilenameExtension

IPython/nbconvert/exporters/exporter.py

@@ -24,7 +24,7 class ResourcesDict(collections.defaultdict):
         return ''
 
 
-class Extension(TraitType):
+class FilenameExtension(TraitType):
     """A trait for filename extensions."""
 
     default_value = u''
@@ -52,7 +52,7 class Exporter(LoggingConfigurable):
     accompanying resources dict.
     """
 
-    file_extension = Extension(
+    file_extension = FilenameExtension(
         '.txt', config=True,
         help="Extension of the file that should be written to disk"
         )