added module 'message.py'

chatmastermind/message.py

@@ -0,0 +1,26 @@
+"""
+Module implementing message related functions and classes.
+"""
+from typing import Type, TypeVar
+
+QuestionInst = TypeVar('QuestionInst', bound='Question')
+
+
+class MessageError(Exception):
+    pass
+
+
+class Question(str):
+    """
+    A single question with a defined prefix.
+    """
+    prefix = '=== QUESTION ==='
+
+    def __new__(cls: Type[QuestionInst], string: str) -> QuestionInst:
+        """
+        Make sure the question string does not contain the prefix.
+        """
+        if cls.prefix in string:
+            raise MessageError(f"Question '{string}' contains the prefix '{cls.prefix}'")
+        instance = super().__new__(cls, string)
+        return instance