Fix exception causes all over the codebase

notebook/bundler/handlers.py

@@ -59,9 +59,10 @@ def get(self, path):
 
         try:
             bundler = self.get_bundler(bundler_id)
-        except KeyError:
-            raise web.HTTPError(400, 'Bundler %s not enabled' % bundler_id)
-
+        except KeyError as e:
+            raise web.HTTPError(400, 'Bundler %s not enabled' %
+                                bundler_id) from e
+
         module_name = bundler['module_name']
         try:
             # no-op in python3, decode error in python2
@@ -72,8 +73,9 @@ def get(self, path):
 
         try:
             bundler_mod = import_item(module_name)
-        except ImportError:
-            raise web.HTTPError(500, 'Could not import bundler %s ' % bundler_id)
+        except ImportError as e:
+            raise web.HTTPError(500, 'Could not import bundler %s ' %
+                                bundler_id) from e
 
         # Let the bundler respond in any way it sees fit and assume it will
         # finish the request

notebook/gateway/managers.py

@@ -282,18 +282,23 @@ def gateway_request(endpoint, **kwargs):
     # or the server is not running.
     # NOTE: We do this here since this handler is called during the Notebook's startup and subsequent refreshes
     # of the tree view.
-    except ConnectionRefusedError:
-        raise web.HTTPError(503, "Connection refused from Gateway server url '{}'.  " 
-              "Check to be sure the Gateway instance is running.".format(GatewayClient.instance().url))
+    except ConnectionRefusedError as e:
+        raise web.HTTPError(
+            503,
+            "Connection refused from Gateway server url '{}'.  Check to be sure the"
+            " Gateway instance is running.".format(GatewayClient.instance().url)
+        ) from e
     except HTTPError as e:
         # This can occur if the host is valid (e.g., foo.com) but there's nothing there.
         raise web.HTTPError(e.code, "Error attempting to connect to Gateway server url '{}'.  "
                        "Ensure gateway url is valid and the Gateway instance is running.".
-                            format(GatewayClient.instance().url))
-    except gaierror:
-        raise web.HTTPError(404, "The Gateway server specified in the gateway_url '{}' doesn't appear to be valid.  "
-                       "Ensure gateway url is valid and the Gateway instance is running.".
-                            format(GatewayClient.instance().url))
+                            format(GatewayClient.instance().url)) from e
+    except gaierror as e:
+        raise web.HTTPError(
+            404,
+            "The Gateway server specified in the gateway_url '{}' doesn't appear to be valid.  Ensure gateway "
+            "url is valid and the Gateway instance is running.".format(GatewayClient.instance().url)
+        ) from e
 
     raise gen.Return(response)
 
@@ -575,8 +580,10 @@ def get_kernel_spec(self, kernel_name, **kwargs):
             if error.status_code == 404:
                 # Convert not found to KeyError since that's what the Notebook handler expects
                 # message is not used, but might as well make it useful for troubleshooting
-                raise KeyError('kernelspec {kernel_name} not found on Gateway server at: {gateway_url}'.
-                               format(kernel_name=kernel_name, gateway_url=GatewayClient.instance().url))
+                raise KeyError(
+                    'kernelspec {kernel_name} not found on Gateway server at: {gateway_url}'.
+                    format(kernel_name=kernel_name, gateway_url=GatewayClient.instance().url)
+                ) from error
             else:
                 raise
         else:

notebook/kernelspecs/handlers.py

@@ -13,8 +13,9 @@ def get(self, kernel_name, path, include_body=True):
         ksm = self.kernel_spec_manager
         try:
             self.root = ksm.get_kernel_spec(kernel_name).resource_dir
-        except KeyError:
-            raise web.HTTPError(404, u'Kernel spec %s not found' % kernel_name)
+        except KeyError as e:
+            raise web.HTTPError(404,
+                                u'Kernel spec %s not found' % kernel_name) from e
         self.log.debug("Serving kernel resource from: %s", self.root)
         return web.StaticFileHandler.get(self, path, include_body=include_body)
 

notebook/nbconvert/handlers.py

@@ -61,19 +61,19 @@ def get_exporter(format, **kwargs):
     try:
         from nbconvert.exporters.base import get_exporter
     except ImportError as e:
-        raise web.HTTPError(500, "Could not import nbconvert: %s" % e)
+        raise web.HTTPError(500, "Could not import nbconvert: %s" % e) from e
 
     try:
         Exporter = get_exporter(format)
-    except KeyError:
+    except KeyError as e:
         # should this be 400?
-        raise web.HTTPError(404, u"No exporter for format: %s" % format)
+        raise web.HTTPError(404, u"No exporter for format: %s" % format) from e
 
     try:
         return Exporter(**kwargs)
     except Exception as e:
         app_log.exception("Could not construct Exporter: %s", Exporter)
-        raise web.HTTPError(500, "Could not construct Exporter: %s" % e)
+        raise web.HTTPError(500, "Could not construct Exporter: %s" % e) from e
 
 class NbconvertFileHandler(IPythonHandler):
 
@@ -133,7 +133,7 @@ def get(self, format, path):
             )
         except Exception as e:
             self.log.exception("nbconvert failed: %s", e)
-            raise web.HTTPError(500, "nbconvert failed: %s" % e)
+            raise web.HTTPError(500, "nbconvert failed: %s" % e) from e
 
         if respond_zip(self, name, output, resources):
             return
@@ -175,7 +175,7 @@ def post(self, format):
                 "config_dir": self.application.settings['config_dir'],
             })
         except Exception as e:
-            raise web.HTTPError(500, "nbconvert failed: %s" % e)
+            raise web.HTTPError(500, "nbconvert failed: %s" % e) from e
 
         if respond_zip(self, name, output, resources):
             return

notebook/notebookapp.py

@@ -54,12 +54,12 @@
 # check for tornado 3.1.0
 try:
     import tornado
-except ImportError:
-    raise ImportError(_("The Jupyter Notebook requires tornado >= 5.0"))
+except ImportError as e:
+    raise ImportError(_("The Jupyter Notebook requires tornado >= 5.0")) from e
 try:
     version_info = tornado.version_info
-except AttributeError:
-    raise ImportError(_("The Jupyter Notebook requires tornado >= 5.0, but you have < 1.1.0"))
+except AttributeError as e:
+    raise ImportError(_("The Jupyter Notebook requires tornado >= 5.0, but you have < 1.1.0")) from e
 if version_info < (5,0):
     raise ImportError(_("The Jupyter Notebook requires tornado >= 5.0, but you have %s") % tornado.version)
 
@@ -858,14 +858,14 @@ def _validate_sock_mode(self, proposal):
                 # And isn't out of bounds.
                 converted_value <= 2 ** 12
             ))
-        except ValueError:
+        except ValueError as e:
             raise TraitError(
                 'invalid --sock-mode value: %s, please specify as e.g. "0600"' % value
-            )
-        except AssertionError:
+            ) from e
+        except AssertionError as e:
             raise TraitError(
                 'invalid --sock-mode value: %s, must have u+rw (0600) at a minimum' % value
-            )
+            ) from e
         return value
 
 

notebook/services/contents/fileio.py

@@ -226,7 +226,7 @@ def perm_to_403(self, os_path=''):
                 if not os_path:
                     os_path = str_to_unicode(e.filename or 'unknown file')
                 path = to_api_path(os_path, root=self.root_dir)
-                raise HTTPError(403, u'Permission denied: %s' % path)
+                raise HTTPError(403, u'Permission denied: %s' % path) from e
             else:
                 raise
 
@@ -310,13 +310,13 @@ def _read_file(self, os_path, format):
             # was explicitly requested.
             try:
                 return bcontent.decode('utf8'), 'text'
-            except UnicodeError:
+            except UnicodeError as e:
                 if format == 'text':
                     raise HTTPError(
                         400,
                         "%s is not UTF-8 encoded" % os_path,
                         reason='bad format',
-                    )
+                    ) from e
         return encodebytes(bcontent).decode('ascii'), 'base64'
 
     def _save_file(self, os_path, content, format):
@@ -335,7 +335,7 @@ def _save_file(self, os_path, content, format):
         except Exception as e:
             raise HTTPError(
                 400, u'Encoding error saving %s: %s' % (os_path, e)
-            )
+            ) from e
 
         with self.atomic_writing(os_path, text=False) as f:
             f.write(bcontent)

notebook/services/contents/filemanager.py

@@ -131,7 +131,8 @@ def run_post_save_hook(self, model, os_path):
                 self.post_save_hook(os_path=os_path, model=model, contents_manager=self)
             except Exception as e:
                 self.log.error("Post-save hook failed o-n %s", os_path, exc_info=True)
-                raise web.HTTPError(500, u'Unexpected error while running post hook save: %s' % e)
+                raise web.HTTPError(500, u'Unexpected error while running post hook save: %s'
+                                    % e) from e
 
     @validate('root_dir')
     def _validate_root_dir(self, proposal):
@@ -487,7 +488,8 @@ def save(self, model, path=''):
             raise
         except Exception as e:
             self.log.error(u'Error while saving file: %s %s', path, e, exc_info=True)
-            raise web.HTTPError(500, u'Unexpected error while saving file: %s %s' % (path, e))
+            raise web.HTTPError(500, u'Unexpected error while saving file: %s %s' %
+                                (path, e)) from e
 
         validation_message = None
         if model['type'] == 'notebook':
@@ -584,7 +586,8 @@ def rename_file(self, old_path, new_path):
         except web.HTTPError:
             raise
         except Exception as e:
-            raise web.HTTPError(500, u'Unknown error renaming file: %s %s' % (old_path, e))
+            raise web.HTTPError(500, u'Unknown error renaming file: %s %s' %
+                                (old_path, e)) from e
 
     def info_string(self):
         return _("Serving notebooks from local directory: %s") % self.root_dir

notebook/services/contents/largefilemanager.py

@@ -34,7 +34,7 @@ def save(self, model, path=''):
                 raise
             except Exception as e:
                 self.log.error(u'Error while saving file: %s %s', path, e, exc_info=True)
-                raise web.HTTPError(500, u'Unexpected error while saving file: %s %s' % (path, e))
+                raise web.HTTPError(500, u'Unexpected error while saving file: %s %s' % (path, e)) from e
 
             model = self.get(path, content=False)
 
@@ -61,7 +61,7 @@ def _save_large_file(self, os_path, content, format):
         except Exception as e:
             raise web.HTTPError(
                 400, u'Encoding error saving %s: %s' % (os_path, e)
-            )
+            ) from e
 
         with self.perm_to_403(os_path):
             if os.path.islink(os_path):

notebook/services/kernelspecs/handlers.py

@@ -87,8 +87,8 @@ def get(self, kernel_name):
         kernel_name = url_unescape(kernel_name)
         try:
             spec = yield maybe_future(ksm.get_kernel_spec(kernel_name))
-        except KeyError:
-            raise web.HTTPError(404, u'Kernel spec %s not found' % kernel_name)
+        except KeyError as e:
+            raise web.HTTPError(404, u'Kernel spec %s not found' % kernel_name) from e
         if is_kernelspec_model(spec):
             model = spec
         else:

notebook/services/nbconvert/handlers.py

@@ -13,7 +13,7 @@ def get(self):
         try:
             from nbconvert.exporters import base
         except ImportError as e:
-            raise web.HTTPError(500, "Could not import nbconvert: %s" % e)
+            raise web.HTTPError(500, "Could not import nbconvert: %s" % e) from e
         res = {}
         exporters = base.get_export_names()
         for exporter_name in exporters:

notebook/services/sessions/handlers.py

@@ -44,13 +44,13 @@ def post(self):
 
         try:
             path = model['path']
-        except KeyError:
-            raise web.HTTPError(400, "Missing field in JSON data: path")
+        except KeyError as e:
+            raise web.HTTPError(400, "Missing field in JSON data: path") from e
 
         try:
             mtype = model['type']
-        except KeyError:
-            raise web.HTTPError(400, "Missing field in JSON data: type")
+        except KeyError as e:
+            raise web.HTTPError(400, "Missing field in JSON data: type") from e
 
         name = model.get('name', None)
         kernel = model.get('kernel', {})
@@ -155,9 +155,9 @@ def delete(self, session_id):
         sm = self.session_manager
         try:
             yield maybe_future(sm.delete_session(session_id))
-        except KeyError:
+        except KeyError as e:
             # the kernel was deleted but the session wasn't!
-            raise web.HTTPError(410, "Kernel deleted before session")
+            raise web.HTTPError(410, "Kernel deleted before session") from e
         self.set_status(204)
         self.finish()
 

notebook/tests/launchnotebook.py

@@ -56,7 +56,7 @@ def wait_until_alive(cls):
                 cls.fetch_url(url)
             except Exception as e:
                 if not cls.notebook_thread.is_alive():
-                    raise RuntimeError("The notebook server failed to start")
+                    raise RuntimeError("The notebook server failed to start") from e
                 time.sleep(POLL_INTERVAL)
             else:
                 return

notebook/tests/selenium/quick_selenium.py

@@ -27,7 +27,7 @@ def quick_driver(lab=False):
         server = list(list_running_servers())[0]
     except IndexError as e:
         raise NoServerError('You need a server running before you can run '
-                            'this command')
+                            'this command') from e
     driver = Firefox()
     auth_url = '{url}?token={token}'.format(**server)
     driver.get(auth_url)