Add --save-on-error flag, closes #626

nbconvert/nbconvertapp.py

@@ -72,6 +72,13 @@ def validate(self, obj, value):
          "(the default behaviour is to abort conversion). This flag "
          "is only relevant if '--execute' was specified, too.")
         ),
+    'save-on-error' : (
+        {'ExecutePreprocessor' : {'save_on_error' : True}},
+        ("Saves the notebook even if one cell throws "
+         "an error. The error message is shown in the cell output."
+         "(the default behaviour is to not save the notebook on an error). This flag "
+         "is only relevant if '--execute' was specified, too.")
+    ),
     'stdin' : (
         {'NbConvertApp' : {
             'from_stdin' : True,

nbconvert/preprocessors/execute.py

@@ -146,6 +146,15 @@ class ExecutePreprocessor(Preprocessor):
         )
     ).tag(config=True)
 
+    save_on_error = Bool(False,
+        help=dedent(
+            """
+            If `False` (default), when a cell raises an error no output is saved.
+            If `True`, the output of the notebook will be saved when an error occors.
+            """
+        )
+    ).tag(config=True)
+
     extra_arguments = List(Unicode())
 
     kernel_name = Unicode('',
@@ -276,6 +285,12 @@ def start_new_kernel(startup_timeout=60, kernel_name='python', **kwargs):
 
         try:
             nb, resources = super(ExecutePreprocessor, self).preprocess(nb, resources)
+        except CellExecutionError:
+            if self.save_on_error:
+                pass
+            else:
+                raise
+
         finally:
             self.kc.stop_channels()
             self.km.shutdown_kernel(now=self.shutdown_kernel == 'immediate')

nbconvert/preprocessors/tests/test_execute.py

@@ -211,6 +211,16 @@ def test_allow_errors(self):
             else:
                 assert u"# üñîçø∂é".encode('utf8', 'replace') in str(exc.value)
 
+    def test_save_on_error(self):
+        """
+        Check that conversion halts if ``allow_errors`` is False.
+        """
+        current_dir = os.path.dirname(__file__)
+        filename = os.path.join(current_dir, 'files', 'Skip Exceptions.ipynb')
+        res = self.build_resources()
+        res['metadata']['path'] = os.path.dirname(filename)
+        self.run_notebook(filename, dict(save_on_error=True), res)
+
     def test_force_raise_errors(self):
         """
         Check that conversion halts if the ``force_raise_errors`` traitlet on