Make use of the raise ... from syntax in Python 3

Author: Cito

.pylintrc

@@ -24,7 +24,6 @@ disable =
  missing-docstring,
  no-self-use,
  protected-access,
- raise-missing-from,
  redefined-argument-from-local,
  redefined-outer-name
 

webware/Application.py

@@ -486,7 +486,7 @@ def createSessionForTransaction(self, trans):
             except KeyError:
                 trans.request().setSessionExpired(1)
                 if not self.setting('IgnoreInvalidSession'):
-                    raise HTTPSessionExpired
+                    raise HTTPSessionExpired from None
                 sessId = None
         if not sessId:
             session = self._sessionClass(trans)

webware/MiscUtils/Configurable.py

@@ -70,9 +70,10 @@ def setting(self, name, default=NoDefault):
         if default is NoDefault:
             try:
                 return self.config()[name]
-            except KeyError:
+            except KeyError as e:
                 keys = ', '.join(sorted(self.config()))
-                raise KeyError(f'{name} not found - config keys are: {keys}')
+                raise KeyError(
+                    f'{name} not found - config keys are: {keys}') from e
         else:
             return self.config().get(name, default)
 
@@ -154,7 +155,7 @@ def userConfig(self):
                 del config[key]
         except Exception as e:
             raise ConfigurationError(
-                f'Invalid configuration file, {filename} ({e}).')
+                f'Invalid configuration file, {filename} ({e}).') from e
         return config
 
     @staticmethod

webware/MiscUtils/DataTable.py

@@ -302,7 +302,7 @@ def setType(self, type_):
             except Exception:
                 types = ', '.join(sorted(_types))
                 raise DataTableError(f'Unknown type {type_!r}.'
-                                     f' Known types are: {types}')
+                                     f' Known types are: {types}') from None
         else:
             self._type = None
 
@@ -699,9 +699,9 @@ def __init__(self, table, values=None, headings=None):
             else:
                 try:
                     self.initFromObject(values)
-                except AttributeError:
+                except AttributeError as e:
                     raise DataTableError(
-                        f'Unknown type for values {values!r}.')
+                        f'Unknown type for values {values!r}.') from e
 
     def initFromSequence(self, values):
         headings = self._headings
@@ -762,7 +762,7 @@ def __getitem__(self, key):
             return self._values[key]
         except TypeError:
             raise TypeError(f'key={key!r}, key type={type(key)!r},'
-                            f' values={self._values!r}')
+                            f' values={self._values!r}') from None
 
     def __setitem__(self, key, value):
         if isinstance(key, str):

webware/MiscUtils/DateInterval.py

@@ -60,5 +60,5 @@ def timeDecode(s):
         try:
             time += int(match[:-1]) * timeValues[char]
         except KeyError:
-            raise ValueError(f'Invalid unit of time: {char}')
+            raise ValueError(f'Invalid unit of time: {char}') from None
     return time

webware/MiscUtils/NamedValueAccess.py

@@ -62,7 +62,7 @@ def valueForKey(obj, key, default=NoDefault):
             try:
                 return obj[key]
             except KeyError:
-                raise ValueForKeyError(key)
+                raise ValueForKeyError(key) from None
         else:
             return obj.get(key, default)
     else:

webware/MiscUtils/PickleRPC.py

@@ -373,9 +373,9 @@ class SafeTransport(Transport):
 
     def make_connection(self, host, port=None, key_file=None, cert_file=None):
         """Create an HTTPS connection object from a host descriptor."""
-        import http.client
         try:
-            return http.client.HTTPSConnection(host, port, key_file, cert_file)
-        except AttributeError:
+            from http.client import HTTPSConnection
+        except ImportError as e:
             raise NotImplementedError(
-                "Your version of http.client doesn't support HTTPS")
+                "Your version of http.client doesn't support HTTPS") from e
+        return HTTPSConnection(host, port, key_file, cert_file)

webware/PSP/PSPParser.py

@@ -172,8 +172,9 @@ def checkScript(self, handler, reader):
         start = reader.mark()
         try:
             stop = reader.skipUntil('%>')
-        except EOFError:
-            raise EOFError("Reached EOF while looking for ending script tag")
+        except EOFError as e:
+            raise EOFError(
+                "Reached EOF while looking for ending script tag") from e
         if stop is None:
             raise PSPParserException('Script not terminated')
         handler.setTemplateInfo(self.tmplStart, self.tmplStop)
@@ -201,9 +202,10 @@ def foo(): return 'foo'
             if stop is None:
                 raise PSPParserException(
                     'Script not terminated in <psp:file> block')
-        except EOFError:
+        except EOFError as e:
             raise EOFError(
-                'Reached EOF while looking for ending script tag </psp:file>')
+                'Reached EOF while looking for'
+                ' ending script tag </psp:file>') from e
         handler.setTemplateInfo(self.tmplStart, self.tmplStop)
         handler.handleScriptFile(start, stop, None)
         return True
@@ -228,9 +230,10 @@ def foo(self):
             if stop is None:
                 raise PSPParserException(
                     'Script not terminated in <psp:class> block')
-        except EOFError:
+        except EOFError as e:
             raise EOFError(
-                'Reached EOF while looking for ending script tag </psp:class>')
+                'Reached EOF while looking for'
+                ' ending script tag </psp:class>') from e
         handler.setTemplateInfo(self.tmplStart, self.tmplStop)
         handler.handleScriptClass(start, stop, None)
         return True

webware/PSP/PSPServletFactory.py

@@ -87,7 +87,8 @@ def loadClassFromFile(self, transaction, fileName, className):
             return getattr(module, className)
         except AttributeError:
             raise AttributeError(
-                f'Cannot find expected class named {className} in {fileName}.')
+                'Cannot find expected class'
+                f' named {className} in {fileName}.') from None
 
     def loadClass(self, transaction, path):
         className = self.computeClassName(path)

webware/PSP/PSPUtils.py

@@ -42,7 +42,7 @@ def checkAttributes(tagType, attrs, validAttrs):
             attrs.remove(attr)
         except KeyError:
             raise PSPParserException(
-                f'{tagType}: Mandatory attribute {attr} missing')
+                f'{tagType}: Mandatory attribute {attr} missing') from None
     optionalAttrs = validAttrs[1]
     for attr in attrs:
         if attr not in optionalAttrs:

webware/PSP/ParseEventHandler.py

@@ -205,8 +205,8 @@ def handleDirective(self, directive, start, stop, attrs):
             encoding = attrs.get('encoding')
             try:
                 self._reader.pushFile(filename, encoding)
-            except IOError:
-                raise IOError(f'PSP include file not found: {filename}')
+            except IOError as e:
+                raise IOError(f'PSP include file not found: {filename}') from e
         else:
             raise ValueError('Invalid directive: {directive}')
 

webware/PickleRPCServlet.py

@@ -89,10 +89,10 @@ def respondToPost(self, trans):
                             try:
                                 rawstring = data.read()
                                 req = self.loads(zlib.decompress(rawstring))
-                            except zlib.error:
+                            except zlib.error as e:
                                 raise RequestError(
                                     'Cannot uncompress'
-                                    ' compressed dict-rpc request')
+                                    ' compressed dict-rpc request') from e
                         else:
                             raise RequestError(
                                 'Cannot handle compressed dict-rpc request')
@@ -101,8 +101,9 @@ def respondToPost(self, trans):
                             f'Cannot handle Content-Encoding of {encoding}')
                     else:
                         req = self.load(data)
-                except PickleError:
-                    raise RequestError('Cannot unpickle dict-rpc request.')
+                except PickleError as e:
+                    raise RequestError(
+                        'Cannot unpickle dict-rpc request.') from e
                 if not isinstance(req, dict):
                     raise RequestError(
                         'Expecting a dictionary for dict-rpc requests, '
@@ -116,7 +117,8 @@ def respondToPost(self, trans):
                 try:
                     methodName = req['methodName']
                 except KeyError:
-                    raise RequestError('Missing method in request')
+                    raise RequestError(
+                        'Missing method name in request') from None
                 args = req.get('args', ())
                 if methodName == '__methods__.__getitem__':
                     # support PythonWin autoname completion

webware/Scripts/WaitressServer.py

@@ -8,8 +8,8 @@
 def serve(args):
     try:
         from waitress import serve
-    except ImportError:
-        raise RuntimeError('Waitress server is not installed')
+    except ImportError as e:
+        raise RuntimeError('Waitress server is not installed') from e
 
     if args.browser:
         scheme = args.url_scheme
@@ -34,8 +34,9 @@ def openBrowser():
     if args.reload:
         try:
             import hupper
-        except ImportError:
-            raise RuntimeError('The hupper process monitor is not installed')
+        except ImportError as e:
+            raise RuntimeError(
+                'The hupper process monitor is not installed') from e
         if not hupper.is_active():
             print('Running Webware with reloading option...')
             args.browser = args.reload = False
@@ -64,8 +65,8 @@ def openBrowser():
         application = scriptVars['application']
     except Exception as e:
         raise RuntimeError(
-            f'Cannot find Webware application:\n{e}\n'
-            'Is the current directory the application working directory?')
+            'Cannot find Webware application.\nIs the current directory'
+            ' the application working directory?') from e
 
     print("Waitress serving Webware application...")
     args = vars(args)

webware/Servlet.py

@@ -3,7 +3,7 @@
 import os
 
 from MiscUtils import AbstractError
-from MiscUtils.Funcs import asclocaltime, excstr
+from MiscUtils.Funcs import asclocaltime
 
 
 class Servlet:
@@ -80,8 +80,7 @@ def runTransaction(transaction):
                 # the first exception gets hidden by the second which is often
                 # just a result of the first. Then you're stuck scratching your
                 # head wondering what the first might have been.
-                raise Exception('Two exceptions. first={}; second={}'.format(
-                    excstr(first), excstr(second)))
+                raise second from first
             else:
                 # no problems with sleep() so raise the one and only exception
                 raise

webware/SessionFileStore.py

@@ -47,21 +47,21 @@ def __getitem__(self, key):
         with self._lock:
             try:
                 sessionFile = open(filename, 'rb')
-            except IOError:
-                raise KeyError(key)  # session file not found
+            except IOError as e:
+                raise KeyError(key) from e  # session file not found
             try:
                 try:
                     value = self.decoder()(sessionFile)
                 finally:
                     sessionFile.close()
-            except Exception:
+            except Exception as e:
                 print("Error loading session from disk:", key)
                 self.application().handleException()
                 try:  # remove the session file because it is corrupt
                     os.remove(filename)
                 except Exception:
                     pass
-                raise KeyError(key)
+                raise KeyError(key) from e
         return value
 
     def __setitem__(self, key, value):

webware/SessionMemcachedStore.py

@@ -5,9 +5,10 @@
 
 try:
     import memcache  # pylint: disable=import-error
-except Exception:
+except Exception as e:
     raise ImportError(
-        "For using Memcached sessions, python-memcached must be installed.")
+        "For using Memcached sessions,"
+        " python-memcached must be installed.") from e
 
 from MiscUtils import NoDefault
 

webware/SessionRedisStore.py

@@ -4,8 +4,10 @@
 
 try:
     import redis  # pylint: disable=import-error
-except Exception:
-    raise ImportError("For using Redis sessions, redis-py must be installed.")
+except Exception as e:
+    raise ImportError(
+        "For using Redis sessions,"
+        " redis-py must be installed.") from e
 
 from MiscUtils import NoDefault
 

webware/SessionStore.py

@@ -198,8 +198,9 @@ def cleanStaleSessions(self, _task=None):
                             timeout == 0 or
                             curTime >= session.lastAccessTime() + timeout):
                         keys.append(key)
-                except AttributeError:
-                    raise ValueError('Not a Session object: %r' % session)
+                except AttributeError as e:
+                    raise ValueError(
+                        f'Not a Session object: {session!r}') from e
         for key in keys:
             try:
                 del self[key]

webware/UnknownFileTypeServlet.py

@@ -189,8 +189,8 @@ def serveContent(self, trans):
         filename = self.filename(trans)
         try:
             f = open(filename, 'rb')
-        except IOError:
-            raise HTTPExceptions.HTTPNotFound
+        except IOError as e:
+            raise HTTPExceptions.HTTPNotFound from e
 
         stat = os.fstat(f.fileno())
         fileSize, mtime = stat[6], stat[8]

webware/WSGIStreamOut.py

@@ -62,7 +62,7 @@ def startResponse(self, status, headers):
                         ' Try the setting WSGIWrite=False.')
         except Exception as e:
             print("Response Start Error:", e)
-            raise ConnectionAbortedError
+            raise ConnectionAbortedError from e
 
     def autoCommit(self):
         """Get the auto commit mode."""
@@ -109,7 +109,7 @@ def flush(self):
             except Exception as e:
                 print("StreamOut Error:", e)
                 self._closed = True
-                raise ConnectionAbortedError
+                raise ConnectionAbortedError from e
             sent += bufferSize
         self.pop(sent)