add TT-entails algorithm

Author: mahidhiman12

machine_learning/ttentails.py

@@ -8,6 +8,20 @@
 """
 
 import itertools
+import re
+
+
+def safe_eval(expr: str, model: dict[str, bool]) -> bool:
+    """Safely evaluate propositional logic expression with given model."""
+    # Replace symbols (like P, Q) with their boolean values
+    for sym, val in model.items():
+        expr = re.sub(rf'\b{sym}\b', str(val), expr)
+    # Allow only True/False, and/or/not operators
+    allowed = {"True", "False", "and", "or", "not", "(", ")", " "}
+    if not all(token in allowed or token.isidentifier() or token in "()" for token in re.split(r'(\W+)', expr)):
+        raise ValueError("Unsafe expression detected")
+    return eval(expr, {"__builtins__": {}}, {})
+
 
 def tt_entails(kb: list[str], query: str, symbols: list[str]) -> bool:
     """
@@ -29,7 +43,7 @@ def tt_entails(kb: list[str], query: str, symbols: list[str]) -> bool:
         model: dict[str, bool] = dict(zip(symbols, values))
         # Check if KB is true under this model
         # # If query is false in this model, KB does not entail query
-        if all(eval(sentence, {}, model) for sentence in kb) and not eval(query, {}, model):
+        if all(safe_eval(sentence, model) for sentence in kb) and not safe_eval(query, model):
             return False
     return True