Allow to build a converter without input file

converters/base.py

@@ -29,7 +29,8 b' from types import FunctionType'
 # IPython imports
 from IPython.nbformat import current as nbformat
 from IPython.config.configurable import Configurable, SingletonConfigurable
-from IPython.utils.traitlets import List, Unicode, Type, Bool, Dict, CaselessStrEnum
+from IPython.utils.traitlets import (List, Unicode, Type, Bool, Dict, CaselessStrEnum,
+                                    Any)
 
 # Our own imports
 from .utils import remove_fake_files_url
@@ -112,7 +113,7 b' class Converter(Configurable):'
     # Instance-level attributes that are set in the constructor for this
     # class.
     #-------------------------------------------------------------------------
-    infile = Unicode()
+    infile = Any()
 
     highlight_source = Bool(True,
                      config=True,
@@ -121,6 +122,7 b' class Converter(Configurable):'
     preamble = Unicode("" ,
                         config=True,
                         help="Path to a user-specified preamble file")
+
     extract_figures = Bool( True,
                             config=True,
                             help="""extract base-64 encoded figures of the notebook into separate files,
@@ -154,6 +156,7 b' class Converter(Configurable):'
         # keep in this way for readability's sake.
         self.exclude_cells = exclude
         self.infile = infile
+        if infile:
         self.infile_dir, infile_root = os.path.split(infile)
         self.infile_root = os.path.splitext(infile_root)[0]
         self.clean_name = clean_filename(self.infile_root)