refactor: update return types to Union[str, None] for better type checking

src/database.py

@@ -1,5 +1,6 @@
 import sqlite3 as sql
 from src.utils import SignatureType
+from typing import Union
 MA_TABLE = """
 CREATE TABLE IF NOT EXISTS ma (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
@@ -34,7 +35,7 @@ class Database:
         cursor.execute(MC_TABLE)
         self.connection.commit()
 
-    def create_new_signature(self, table:str)->str:
+    def create_new_signature(self, table: str) -> Union[str, None]:
         """Create a new signature for the given table.
         The new signature is generated by using 01 / as prefix, then incrementing the number by 1 for each new entry."""
         cursor = self.connection.cursor()
@@ -51,7 +52,7 @@ class Database:
         count = cursor.fetchone()[0]
         return count > 0
 
-    def insert(self, old_signature: str) -> str | None:
+    def insert(self, old_signature: str) -> Union[str, None]:
         table = old_signature.split(" ")[0].lower()
         if table == "ma":
             return self.insert_ma(old_signature)
@@ -63,7 +64,7 @@ class Database:
             # print(f"Error: Unknown signature type '{table}'. Please use 'ma', 'mb', or 'mc'.")
             return self.insert_ma(old_signature)
 
-    def get_signature(self, old_signature: str, table: str) -> str | None:
+    def get_signature(self, old_signature: str, table: str) -> Union[str, None]:
         """Get the new signature for the given old signature from the specified table."""
         cursor = self.connection.cursor()
         cursor.execute(
@@ -79,7 +80,7 @@ class Database:
             )
             return None
 
-    def insert_ma(self, old_signature: str) -> str|None:
+    def insert_ma(self, old_signature: str) -> Union[str, None]:
         """Insert an old signature into the ma table and return the new signature.
         New Signatures is generated by using 01 / as prefix, then incrementing the number by 1 for each new entry."""
         if self.signature_exists(old_signature, "ma"):
@@ -96,8 +97,7 @@ class Database:
             print(f"Error: The combination of old_signature '{old_signature}' and new_signature '{new_signature}' already exists.")
             return None
 
-
-    def insert_mb(self, old_signature: str) -> str:
+    def insert_mb(self, old_signature: str) -> Union[str, None]:
         """Insert an old signature into the mb table and return the new signature.
         New Signatures is generated by using 02 / as prefix, then incrementing the number by 1 for each new entry."""
         new_signature = self.create_new_signature("mb")
@@ -115,8 +115,8 @@ class Database:
         except sql.IntegrityError:
             print(f"Error: The combination of old_signature '{old_signature}' and new_signature '{new_signature}' already exists.")
             return None
-        
-    def insert_mc(self, old_signature: str) -> str:
+
+    def insert_mc(self, old_signature: str) -> Union[str, None]:
         """Insert an old signature into the mc table and return the new signature.
         New Signatures is generated by using 03 / as prefix, then incrementing the number by 1 for each new entry."""
         new_signature = self.create_new_signature("mc")