fix: Resolve mypy and ruff linting errors

- Fix type annotation for parse_foreign_key_error to allow None values
- Remove unnecessary f-string prefixes (ruff F541)
- Split long line in postgres.py FK error pattern (ruff E501)
- Fix equality comparison to False in heading.py (ruff E712)
- Remove unused import 're' from table.py (ruff F401)

All unit tests passing (212/212).
All PostgreSQL multi-backend tests passing (4/4).
mypy and ruff checks passing.

Author: dimitri-yatsenko

src/datajoint/adapters/base.py

@@ -628,7 +628,7 @@ def get_constraint_info_sql(self, constraint_name: str, schema_name: str, table_
         ...
 
     @abstractmethod
-    def parse_foreign_key_error(self, error_message: str) -> dict[str, str | list[str]] | None:
+    def parse_foreign_key_error(self, error_message: str) -> dict[str, str | list[str] | None] | None:
         """
         Parse a foreign key violation error message to extract constraint details.
 

src/datajoint/adapters/mysql.py

@@ -598,15 +598,15 @@ def get_foreign_keys_sql(self, schema_name: str, table_name: str) -> str:
     def get_constraint_info_sql(self, constraint_name: str, schema_name: str, table_name: str) -> str:
         """Query to get FK constraint details from information_schema."""
         return (
-            f"SELECT "
-            f"  COLUMN_NAME as fk_attrs, "
-            f"  CONCAT('`', REFERENCED_TABLE_SCHEMA, '`.`', REFERENCED_TABLE_NAME, '`') as parent, "
-            f"  REFERENCED_COLUMN_NAME as pk_attrs "
-            f"FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE "
-            f"WHERE CONSTRAINT_NAME = %s AND TABLE_SCHEMA = %s AND TABLE_NAME = %s"
+            "SELECT "
+            "  COLUMN_NAME as fk_attrs, "
+            "  CONCAT('`', REFERENCED_TABLE_SCHEMA, '`.`', REFERENCED_TABLE_NAME, '`') as parent, "
+            "  REFERENCED_COLUMN_NAME as pk_attrs "
+            "FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE "
+            "WHERE CONSTRAINT_NAME = %s AND TABLE_SCHEMA = %s AND TABLE_NAME = %s"
         )
 
-    def parse_foreign_key_error(self, error_message: str) -> dict[str, str | list[str]] | None:
+    def parse_foreign_key_error(self, error_message: str) -> dict[str, str | list[str] | None] | None:
         """Parse MySQL foreign key violation error message."""
         import re
 

src/datajoint/adapters/postgres.py

@@ -670,21 +670,21 @@ def get_foreign_keys_sql(self, schema_name: str, table_name: str) -> str:
     def get_constraint_info_sql(self, constraint_name: str, schema_name: str, table_name: str) -> str:
         """Query to get FK constraint details from information_schema."""
         return (
-            f"SELECT "
-            f"  kcu.column_name as fk_attrs, "
-            f"  '\"' || ccu.table_schema || '\".\"' || ccu.table_name || '\"' as parent, "
-            f"  ccu.column_name as pk_attrs "
-            f"FROM information_schema.key_column_usage AS kcu "
-            f"JOIN information_schema.constraint_column_usage AS ccu "
-            f"  ON kcu.constraint_name = ccu.constraint_name "
-            f"  AND kcu.constraint_schema = ccu.constraint_schema "
-            f"WHERE kcu.constraint_name = %s "
-            f"  AND kcu.table_schema = %s "
-            f"  AND kcu.table_name = %s "
-            f"ORDER BY kcu.ordinal_position"
+            "SELECT "
+            "  kcu.column_name as fk_attrs, "
+            "  '\"' || ccu.table_schema || '\".\"' || ccu.table_name || '\"' as parent, "
+            "  ccu.column_name as pk_attrs "
+            "FROM information_schema.key_column_usage AS kcu "
+            "JOIN information_schema.constraint_column_usage AS ccu "
+            "  ON kcu.constraint_name = ccu.constraint_name "
+            "  AND kcu.constraint_schema = ccu.constraint_schema "
+            "WHERE kcu.constraint_name = %s "
+            "  AND kcu.table_schema = %s "
+            "  AND kcu.table_name = %s "
+            "ORDER BY kcu.ordinal_position"
         )
 
-    def parse_foreign_key_error(self, error_message: str) -> dict[str, str | list[str]] | None:
+    def parse_foreign_key_error(self, error_message: str) -> dict[str, str | list[str] | None] | None:
         """
         Parse PostgreSQL foreign key violation error message.
 
@@ -697,7 +697,8 @@ def parse_foreign_key_error(self, error_message: str) -> dict[str, str | list[st
         import re
 
         pattern = re.compile(
-            r'.*table "(?P<referenced_table>[^"]+)" violates foreign key constraint "(?P<name>[^"]+)" on table "(?P<referencing_table>[^"]+)"'
+            r'.*table "(?P<referenced_table>[^"]+)" violates foreign key constraint '
+            r'"(?P<name>[^"]+)" on table "(?P<referencing_table>[^"]+)"'
         )
 
         match = pattern.match(error_message)

src/datajoint/heading.py

@@ -558,7 +558,7 @@ def _init_from_database(self) -> None:
 
             keys[index_name][seq] = dict(
                 column=column,
-                unique=(non_unique == 0 or non_unique == False),
+                unique=(non_unique == 0 or not non_unique),
                 nullable=nullable,
             )
         self.indexes = {

src/datajoint/table.py

@@ -4,7 +4,6 @@
 import itertools
 import json
 import logging
-import re
 import uuid
 import warnings
 from dataclasses import dataclass, field