flake8-bugbear: opt-in to a couple of opinionated warnings

cylc/flow/config.py

@@ -2463,21 +2463,21 @@ def get_taskdef(
                             'Duplicate task message in'
                             f' "[runtime][{name}][outputs]'
                             f'{output} = {message}" - messages must be unique'
-                        )
+                        ) from None
                     valid, msg = TaskOutputValidator.validate(output)
                     if not valid:
                         raise WorkflowConfigError(
                             f'Invalid task output "'
                             f'[runtime][{name}][outputs]'
                             f'{output} = {message}" - {msg}'
-                        ) from None
+                        )
                     valid, msg = TaskMessageValidator.validate(message)
                     if not valid:
                         raise WorkflowConfigError(
                             f'Invalid task message "'
                             f'[runtime][{name}][outputs]'
                             f'{output} = {message}" - {msg}'
-                        ) from None
+                        )
                     self.taskdefs[name].add_output(output, message)
 
         return self.taskdefs[name]

cylc/flow/dbstatecheck.py

@@ -78,15 +78,15 @@
         try:
             self.db_point_fmt = self._get_db_point_format()
             self.c7_back_compat_mode = False
-        except sqlite3.OperationalError:
+        except sqlite3.OperationalError as exc:
             # BACK COMPAT: Cylc 7 DB (see method below).
             try:
                 self.db_point_fmt = self._get_db_point_format_compat()
                 self.c7_back_compat_mode = True
             except sqlite3.OperationalError:
                 with suppress(Exception):
                     self.conn.close()
-                raise
+                raise exc from None  # original error
 
     def __enter__(self):
         return self

cylc/flow/main_loop/health_check.py

@@ -52,8 +52,8 @@ def _check_contact_file(scheduler):
             scheduler.workflow)
         if contact_data != scheduler.contact_data:
             raise CylcError('contact file modified')
-    except (AssertionError, IOError, ValueError, ServiceFileError):
+    except (AssertionError, IOError, ValueError, ServiceFileError) as exc:
         raise CylcError(
             '%s: contact file corrupted/modified and may be left'
             % workflow_files.get_contact_file_path(scheduler.workflow)
-        ) from None
+        ) from exc

cylc/flow/network/__init__.py

@@ -176,16 +176,14 @@
                 srv_prv_key_info.full_key_path)
         except ValueError:
             raise ServiceFileError(
-                f"Failed to find server's public "
-                f"key in "
+                "Failed to find server's public key in "
                 f"{srv_prv_key_info.full_key_path}."
             ) from None
-        except OSError:
+        except OSError as exc:
             raise ServiceFileError(
-                f"IO error opening server's private "
-                f"key from "
+                "IO error opening server's private key from "
                 f"{srv_prv_key_info.full_key_path}."
-            ) from None
+            ) from exc
         if server_private_key is None:  # this can't be caught by exception
             raise ServiceFileError(
                 f"Failed to find server's private "
@@ -238,15 +236,20 @@
         try:
             client_public_key, client_priv_key = zmq.auth.load_certificate(
                 client_priv_key_info.full_key_path)
-        except (OSError, ValueError):
+        except ValueError:
             raise ClientError(error_msg) from None
+        except OSError as exc:
+            raise ClientError(error_msg) from exc
         if client_priv_key is None:  # this can't be caught by exception
             raise ClientError(error_msg)
         self.socket.curve_publickey = client_public_key
         self.socket.curve_secretkey = client_priv_key
 
         # A client can only connect to the server if it knows its public key,
         # so we grab this from the location it was created on the filesystem:
+        error_msg = (
+            "Failed to load the workflow's public key, so cannot connect."
+        )
         try:
             # 'load_certificate' will try to load both public & private keys
             # from a provided file but will return None, not throw an error,
@@ -256,10 +259,10 @@
             server_public_key = zmq.auth.load_certificate(
                 srv_pub_key_info.full_key_path)[0]
             self.socket.curve_serverkey = server_public_key
-        except (OSError, ValueError):  # ValueError raised w/ no public key
-            raise ClientError(
-                "Failed to load the workflow's public key, so cannot connect."
-            ) from None
+        except ValueError:  # ValueError raised w/ no public key
+            raise ClientError(error_msg) from None
+        except OSError as exc:
+            raise ClientError(error_msg) from exc
 
         self.socket.connect(f'tcp://{host}:{port}')
 

cylc/flow/param_expand.py

@@ -196,7 +196,7 @@ def _expand_name(self, results, tmpl, params, spec_vals=None):
                 results.append((tmpl % current_values, current_values))
             except KeyError as exc:
                 raise ParamExpandError(
-                    'parameter %s is not ' 'defined.' % str(exc.args[0])
+                    'parameter %s is not defined.' % str(exc.args[0])
                 ) from None
         else:
             for param_val in params[0][1]:
@@ -427,7 +427,7 @@ def _expand_graph(self, line, all_params,
                     repl = tmpl % param_values
                 except KeyError as exc:
                     raise ParamExpandError(
-                        'parameter %s is not ' 'defined.' % str(exc.args[0])
+                        'parameter %s is not defined.' % str(exc.args[0])
                     ) from None
                 line = line.replace('<' + p_group + '>', repl)
             if line:

cylc/flow/scripts/cylc.py

@@ -605,14 +605,14 @@ def pycoverage(cmd_args):  # pragma: no cover
             data_file=str(cylc_wc / '.coverage'),
             source=[str(cylc_wc / 'cylc')]
         )
-    except coverage.misc.CoverageException:
+    except coverage.misc.CoverageException as exc:
         raise Exception(
             # make sure this exception is visible in the traceback
             '\n\n*****************************\n\n'
             'Could not initiate coverage, likely because Cylc was not '
             'installed in editable mode.'
             '\n\n*****************************\n\n'
-        ) from None
+        ) from exc
 
     # start the coverage running
     cov.start()

cylc/flow/scripts/lint.py

@@ -51,53 +51,62 @@
 """
 import functools
 import pkgutil
-from pathlib import Path
 import re
-import sys
 import shutil
+import sys
+from collections import Counter
+from pathlib import Path
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Callable,
+    Counter as CounterType,
+    Dict,
+    Iterator,
+    List,
+    Optional,
+    Union,
+)
+
 try:
     # BACK COMPAT: tomli
     #   Support for Python versions before tomllib was added to the
     #   standard library.
     # FROM: Python 3.7
     # TO: Python: 3.10
-    from tomli import (
-        loads as toml_loads,
-        TOMLDecodeError,
-    )
+    from tomli import TOMLDecodeError, loads as toml_loads
 except ImportError:
     from tomllib import (  # type: ignore[no-redef]
         loads as toml_loads,
         TOMLDecodeError,
     )
-from typing import (
-    TYPE_CHECKING, Any, Callable, Dict, Iterator, List, Optional, Union
-)
 
 from ansimarkup import parse as cparse
 
-from cylc.flow import LOG
-from cylc.flow.exceptions import CylcError
 import cylc.flow.flags
-from cylc.flow import job_runner_handlers
+from cylc.flow import LOG, job_runner_handlers
+from cylc.flow.cfgspec.workflow import SPEC, upg
+from cylc.flow.exceptions import CylcError
+from cylc.flow.id_cli import parse_id
 from cylc.flow.job_runner_mgr import JobRunnerManager
 from cylc.flow.loggingutil import set_timestamps
 from cylc.flow.option_parsers import (
+    WORKFLOW_ID_OR_PATH_ARG_DOC,
     CylcOptionParser as COP,
-    WORKFLOW_ID_OR_PATH_ARG_DOC
 )
-from cylc.flow.cfgspec.workflow import upg, SPEC
-from cylc.flow.id_cli import parse_id
 from cylc.flow.parsec.config import ParsecConfig
 from cylc.flow.scripts.cylc import DEAD_ENDS
 from cylc.flow.terminal import cli_function
 
+
 if TYPE_CHECKING:
+    from optparse import Values
+
     # BACK COMPAT: typing_extensions.Literal
     # FROM: Python 3.7
     # TO: Python 3.8
     from typing_extensions import Literal
-    from optparse import Values
+
 
 LINT_TABLE = ['tool', 'cylc', 'lint']
 LINT_SECTION = '.'.join(LINT_TABLE)
@@ -1114,7 +1123,7 @@ def check_cylc_file(
     file: Path,
     file_rel: Path,
     checks: Dict[str, dict],
-    counter: Dict[str, int],
+    counter: CounterType[str],
     modify: bool = False,
 ):
     """Check A Cylc File for Cylc 7 Config"""
@@ -1172,7 +1181,7 @@ def lint(
     file_rel: Path,
     lines: Iterator[str],
     checks: Dict[str, dict],
-    counter: Dict[str, int],
+    counter: CounterType[str],
     modify: bool = False,
     write: Callable = print
 ) -> Iterator[str]:
@@ -1186,7 +1195,7 @@ def lint(
             Iterator which produces one line of text at a time
             e.g. open(file) or iter(['foo\n', 'bar\n', 'baz\n'].
         counter:
-            Dictionary for counting lint hits per category.
+            Counter for counting lint hits per category.
         modify:
             If True, this generator will yield the file one line at a time
             with comments inserted to help users fix their lint.
@@ -1238,7 +1247,6 @@ def lint(
                     msg = check_meta['short'].format(**check)
                 else:
                     msg = check_meta['short']
-                counter.setdefault(check_meta['purpose'], 0)
                 counter[check_meta['purpose']] += 1
                 if modify:
                     # insert a command to help the user
@@ -1473,7 +1481,7 @@ def main(parser: COP, options: 'Values', target=None) -> None:
     )
 
     # Check each file matching a pattern:
-    counter: Dict[str, int] = {}
+    counter: CounterType[str] = Counter()
     for file in get_cylc_files(target, mergedopts[EXCLUDE]):
         LOG.debug(f'Checking {file}')
         check_cylc_file(

cylc/flow/scripts/report_timings.py

@@ -48,13 +48,12 @@
 the database query to obtain the timing information may take some time.
 """
 
-import collections
 import contextlib
 import io as StringIO
 import sys
+from collections import Counter
 from typing import TYPE_CHECKING
 
-
 from cylc.flow import LOG
 from cylc.flow.exceptions import CylcError
 from cylc.flow.id_cli import parse_id
@@ -66,6 +65,7 @@
 from cylc.flow.rundb import CylcWorkflowDAO
 from cylc.flow.terminal import cli_function
 
+
 if TYPE_CHECKING:
     from optparse import Values
 
@@ -278,7 +278,7 @@ def _reshape_timings(timings):
             # there are duplicate entries in the index (see #2509).  The
             # best way around this seems to be to add an intermediate index
             # level (in this case a retry counter) to de-duplicate indices.
-            counts = collections.defaultdict(int)
+            counts = Counter()
             retry = []
             for t in timings.index:
                 counts[t] += 1

cylc/flow/workflow_db_mgr.py

@@ -700,10 +700,10 @@ def _get_last_run_version(cls, pri_dao: CylcWorkflowDAO) -> Version:
                 ''',  # nosec (table name is a code constant)
                 [cls.KEY_CYLC_VERSION]
             ).fetchone()[0]
-        except (TypeError, OperationalError):
+        except (TypeError, OperationalError) as exc:
             raise ServiceFileError(
                 f"{INCOMPAT_MSG}, or is corrupted."
-            ) from None
+            ) from exc
         return parse_version(last_run_ver)
 
     @classmethod

cylc/flow/workflow_files.py

@@ -634,8 +634,8 @@ def load_contact_file(id_: str, run_dir=None) -> Dict[str, str]:
     try:
         with open(path) as f:
             file_content = f.read()
-    except IOError:
-        raise ServiceFileError("Couldn't load contact file") from None
+    except IOError as exc:
+        raise ServiceFileError("Couldn't load contact file") from exc
     data: Dict[str, str] = {}
     for line in file_content.splitlines():
         key, value = [item.strip() for item in line.split("=", 1)]

cylc/flow/xtrigger_mgr.py

@@ -390,7 +390,7 @@
             bound_args = sig.bind(*fctx.func_args, **fctx.func_kwargs)
         except TypeError:
             # failed signature check for backcompat function
-            raise
+            raise err from None  # original signature check error
 
         old_sig_str = fctx.get_signature()
         upg_sig_str = "workflow_state({})".format(

tests/unit/scripts/test_lint.py

@@ -16,6 +16,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 """Tests `cylc lint` CLI Utility."""
 
+from collections import Counter
 import logging
 from pathlib import Path
 from pprint import pformat
@@ -190,7 +191,7 @@
 
 def lint_text(text, checks, ignores=None, modify=False):
     checks = parse_checks(checks, ignores)
-    counter = {}
+    counter = Counter()
     messages = []
     outlines = [
         line

tox.ini

@@ -1,4 +1,10 @@
 [flake8]
+extend-select=
+    ; Use `raise from` inside `except` for error handling
+    ; https://docs.python.org/3/tutorial/errors.html#exception-chaining
+    B904
+    ; Use Counter() instead of defaultdict(int) to avoid excessive memory use:
+    B910
 ignore=
     ; module level import not at top of file
     E402,