Ruff: enable B904: Use raise from to specify exception cause (PYTHON2.7 COMPAT)

Author: giampaolo

demo/md5_ftpd.py

@@ -25,7 +25,7 @@ def validate_authentication(self, username, password, handler):
             if self.user_table[username]["pwd"] != hash_:
                 raise KeyError
         except KeyError:
-            raise AuthenticationFailed
+            raise AuthenticationFailed from None
 
 
 def main():

pyftpdlib/__main__.py

@@ -59,7 +59,9 @@ def parse_encoding(value):
     try:
         codecs.lookup(value)
     except LookupError:
-        raise argparse.ArgumentTypeError(f"unknown encoding: {value!r}")
+        raise argparse.ArgumentTypeError(
+            f"unknown encoding: {value!r}"
+        ) from None
     return value
 
 
@@ -70,7 +72,7 @@ def parse_port_range(value):
     except ValueError:
         raise argparse.ArgumentTypeError(
             f"invalid port range: {value!r} (expected FROM-TO)"
-        )
+        ) from None
     if not (1 <= start <= 65535 and 1 <= stop <= 65535):
         raise argparse.ArgumentTypeError(
             "port numbers must be between 1 and 65535"

pyftpdlib/authorizers.py

@@ -422,8 +422,10 @@ def __init__(self, anonymous_user=None):
             if self.anonymous_user is not None:
                 try:
                     pwd.getpwnam(self.anonymous_user).pw_dir  # noqa
-                except KeyError:
-                    raise AuthorizerError(f"no such user {anonymous_user}")
+                except KeyError as err:
+                    raise AuthorizerError(
+                        f"no such user {anonymous_user}"
+                    ) from err
 
         # --- overridden / private API
 
@@ -438,8 +440,8 @@ def validate_authentication(self, username, password, handler):
                 try:
                     pw1 = spwd.getspnam(username).sp_pwd
                     pw2 = crypt.crypt(password, pw1)
-                except KeyError:  # no such username
-                    raise AuthenticationFailed(self.msg_no_such_user)
+                except KeyError as err:  # no such username
+                    raise AuthenticationFailed(self.msg_no_such_user) from err
                 else:
                     if pw1 != pw2:
                         raise AuthenticationFailed(self.msg_wrong_password)
@@ -451,8 +453,8 @@ def impersonate_user(self, username, password):
             """
             try:
                 pwdstruct = pwd.getpwnam(username)
-            except KeyError:
-                raise AuthorizerError(self.msg_no_such_user)
+            except KeyError as err:
+                raise AuthorizerError(self.msg_no_such_user) from err
             else:
                 os.setegid(pwdstruct.pw_gid)
                 os.seteuid(pwdstruct.pw_uid)
@@ -475,8 +477,8 @@ def get_home_dir(self, username):
             """Return user home directory."""
             try:
                 return pwd.getpwnam(username).pw_dir
-            except KeyError:
-                raise AuthorizerError(self.msg_no_such_user)
+            except KeyError as err:
+                raise AuthorizerError(self.msg_no_such_user) from err
 
         @staticmethod
         def _get_system_users():
@@ -713,8 +715,8 @@ def validate_authentication(self, username, password, handler):
                     win32con.LOGON32_LOGON_INTERACTIVE,
                     win32con.LOGON32_PROVIDER_DEFAULT,
                 )
-            except pywintypes.error:
-                raise AuthenticationFailed(self.msg_wrong_password)
+            except pywintypes.error as err:
+                raise AuthenticationFailed(self.msg_wrong_password) from err
 
         @replace_anonymous
         def impersonate_user(self, username, password):
@@ -747,15 +749,15 @@ def get_home_dir(self, username):
                     win32security.LookupAccountName(None, username)[0]
                 )
             except pywintypes.error as err:
-                raise AuthorizerError(err)
+                raise AuthorizerError(err) from err
             path = r"SOFTWARE\Microsoft\Windows NT"
             path += r"\CurrentVersion\ProfileList" + "\\" + sid
             try:
                 key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, path)
-            except OSError:
+            except OSError as err:
                 raise AuthorizerError(
                     f"No profile directory defined for user {username}"
-                )
+                ) from err
             value = winreg.QueryValueEx(key, "ProfileImagePath")[0]
             home = win32api.ExpandEnvironmentStrings(value)
             return home

pyftpdlib/handlers.py

@@ -816,7 +816,7 @@ def initiate_sendfile(self):
                 logger.warning(
                     "sendfile() failed; falling back on using plain send"
                 )
-                raise _GiveUpOnSendfile
+                raise _GiveUpOnSendfile from err
             else:
                 raise
         else:
@@ -935,7 +935,7 @@ def handle_read(self):
             try:
                 self.file_obj.write(chunk)
             except OSError as err:
-                raise _FileReadWriteError(err)
+                raise _FileReadWriteError(err) from err
 
     handle_read_event = handle_read  # small speedup
 
@@ -1192,7 +1192,7 @@ def more(self):
         try:
             data = self.file.read(self.buffer_size)
         except OSError as err:
-            raise _FileReadWriteError(err)
+            raise _FileReadWriteError(err) from err
         else:
             if self._data_wrapper is not None:
                 data = self._data_wrapper(data)
@@ -3469,14 +3469,14 @@ def send(self, data):
         def recv(self, buffer_size):
             try:
                 return super().recv(buffer_size)
-            except SSL.WantReadError:
+            except SSL.WantReadError as err:
                 debug("call: recv(), err: ssl-want-read", inst=self)
                 self._ssl_want_read = True
-                raise RetryError
-            except SSL.WantWriteError:
+                raise RetryError from err
+            except SSL.WantWriteError as err:
                 debug("call: recv(), err: ssl-want-write", inst=self)
                 self._ssl_want_write = True
-                raise RetryError
+                raise RetryError from err
             except SSL.ZeroReturnError:
                 debug(
                     "call: recv() -> shutdown(), err: zero-return", inst=self

pyftpdlib/ioloop.py

@@ -949,7 +949,7 @@ def recv(self, buffer_size):
                 self.handle_close()
                 return b""
             elif err.errno in _ERRNOS_RETRY:
-                raise RetryError
+                raise RetryError from err
             else:
                 raise
         else:

pyproject.toml

@@ -27,7 +27,6 @@ ignore = [
     "A",  # flake8-builtins
     "ANN",  # flake8-annotations
     "ARG",  # flake8-unused-arguments
-    "B904",  # Use `raise from` to specify exception cause (PYTHON2.7 COMPAT)
     "BLE001",  # Do not catch blind exception: `Exception`
     "C4",  # flake8-comprehensions (PYTHON2.7 COMPAT)
     # "C408",  # Unnecessary `dict` call (rewrite as a literal)

tests/test_authorizers.py

@@ -230,7 +230,7 @@ def assertRaisesWithMsg(self, excClass, msg, callableObj, *args, **kwargs):
         except excClass as err:
             if str(err) == msg:
                 return
-            raise self.failureException(f"{err!s} != {msg}")
+            raise self.failureException(f"{err!s} != {msg}") from err
         else:
             if hasattr(excClass, "__name__"):
                 excName = excClass.__name__

tests/test_functional_ssl.py

@@ -199,7 +199,7 @@ def assertRaisesWithMsg(self, excClass, msg, callableObj, *args, **kwargs):
         except excClass as err:
             if str(err) == msg:
                 return
-            raise self.failureException(f"{err!s} != {msg}")
+            raise self.failureException(f"{err!s} != {msg}") from err
         else:
             if hasattr(excClass, "__name__"):
                 excName = excClass.__name__