Merge pull request #3759 from jdfreder/help_fix

nbconvert: Provide a more useful error for invalid use case.

We now print the help message if no notebooks were converted

IPython/config/application.py

@@ -88,9 +88,7 b' def catch_config_error(method, app, *args, **kwargs):'
     try:
         return method(app, *args, **kwargs)
     except (TraitError, ArgumentError) as e:
-        app.print_description()
         app.print_help()
-        app.print_examples()
         app.log.fatal("Bad config encountered during initialization:")
         app.log.fatal(str(e))
         app.log.debug("Config at the time: %s", app.config)
@@ -337,6 +335,7 b' class Application(SingletonConfigurable):'
 
         If classes=False (the default), only flags and aliases are printed.
         """
+        self.print_description()
         self.print_subcommands()
         self.print_options()
 
@@ -356,6 +355,9 b' class Application(SingletonConfigurable):'
             print "To see all available configurables, use `--help-all`"
             print
 
+        self.print_examples()
+
+
     def print_description(self):
         """Print the application description."""
         for p in wrap_paragraphs(self.description):
@@ -475,9 +477,7 b' class Application(SingletonConfigurable):'
             interpreted_argv = argv
 
         if any(x in interpreted_argv for x in ('-h', '--help-all', '--help')):
-            self.print_description()
             self.print_help('--help-all' in interpreted_argv)
-            self.print_examples()
             self.exit(0)
 
         if '--version' in interpreted_argv or '-V' in interpreted_argv:

IPython/nbconvert/nbconvertapp.py

@@ -209,24 +209,14 b' class NbConvertApp(BaseIPythonApplication):'
                       "\n\t" + "\n\t".join(get_export_names()),
                       file=sys.stderr)
                 sys.exit(-1)
-            # except Exception as e:
-                # print("Error: could not export '%s'" % notebook_filename, file=sys.stderr)
-                # print(e, file=sys.stderr)
             else:
                 self.writer.write(output, resources, notebook_name=notebook_name)
                 conversion_success += 1
 
         # If nothing was converted successfully, help the user.
         if conversion_success == 0:
-
-            # No notebooks were specified, show help.
-            if len(self.notebooks) == 0:
-                self.print_help()
-
-            # Notebooks were specified, but not converted successfully.  Show how
-            # to access help.
-            else:
-                print('For help, use "ipython nbconvert --help"')
+            self.print_help()
+            sys.exit(-1)
 
 
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