[Sync Iteration] python/wordy/9

solutions/python/wordy/9/wordy.py

@@ -0,0 +1,109 @@
+"""
+Parse and evaluate simple math word problems
+returning the answer as an integer.
+
+Handle a set of operations, in sequence.
+
+Since these are verbal word problems, evaluate
+the expression from left-to-right, ignoring the
+typical order of operations.
+"""
+
+STR_TO_OPERATOR: dict[str, str] = {
+    "plus": "+",
+    "minus": "-",
+    "multiplied": "*",
+    "divided": "/",
+}
+
+REPLACEABLE: tuple = ("What", "is", "by")
+
+
+def answer(question: str) -> int:
+    """
+    Evaluate a simple word-based arithmetic question from left to right.
+
+    :param question: The input question, e.g., "What is 5 plus 13?"
+    :type question: str
+    :returns: The evaluated integer result.
+    :rtype: int
+    :raises ValueError: If the operation is unknown or the syntax is invalid.
+    """
+    new_question: list[str] = [
+        word
+        for word in question.replace("?", "").split()
+        if word not in REPLACEABLE
+    ]
+    # Reduce iteratively:
+    # evaluate the first two-token slice and fold the result left-to-right.
+    try:
+        result, new_question = int(new_question[0]), new_question[1:]
+        while new_question:
+            _err_check(new_question)
+            result, new_question = (
+                _math_operation(result, new_question),
+                new_question[2:],
+            )
+    except ValueError as exc:
+        if exc.args[0] == "unknown operation":
+            raise exc
+        raise ValueError("syntax error") from exc
+    except IndexError as exc:
+        raise ValueError("syntax error") from exc
+
+    return result
+
+
+def _math_operation(result: int, question: list[str]) -> int:
+    """
+    Compute a single binary arithmetic step for the current operator.
+
+    Expects the next tokens of the question to begin with the operator word
+    (e.g. ``plus``, ``minus``, ``multiplied``, ``divided``) followed by the
+    right-hand side operand. Division uses floor division (``//``) to comply
+    with the exercise rules.
+
+    :param result: Accumulated left-hand value computed so far.
+    :type result: int
+    :param question: Remaining tokens starting with the operator then rhs
+                     integer, e.g. ``['plus', '4', ...]``.
+    :type question: list[str]
+    :returns: Accumulated result after consuming the operator and rhs.
+    :rtype: int
+    """
+    math_operator: str = question[0]
+    operand: int = int(question[1])
+
+    match STR_TO_OPERATOR[math_operator]:
+        case "+":
+            result += operand
+        case "-":
+            result -= operand
+        case "/":
+            result //= operand
+        case "*":
+            result *= operand
+
+    return result
+
+
+def _err_check(question: list[str]) -> None:
+    """
+    Validate the upcoming operator/operand tokens and raise appropriate errors.
+
+    :param question: Remaining tokens starting at the operator; used to detect
+                     malformed sequences (e.g., missing rhs integer).
+    :type question: list[str]
+    :raises ValueError: If an unknown operation is encountered or the token
+                        sequence is syntactically invalid.
+    """
+    math_operator: str = question[0]
+    # if the question contains an unknown operation.
+    if math_operator not in STR_TO_OPERATOR and not math_operator.isdigit():
+        raise ValueError("unknown operation")
+    # if the question is malformed or invalid.
+    if math_operator.isdigit():
+        raise ValueError("syntax error")
+    # if the question is malformed or invalid.
+    if math_operator in STR_TO_OPERATOR and len(question) == 1:
+        raise ValueError("syntax error")