Merge pull request #179 from ikostan/exercism-sync/383869105c757f18

[Sync Iteration] python/wordy/5

Author: ikostan

solutions/python/wordy/5/wordy.py

@@ -0,0 +1,159 @@
+"""
+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 = {
+    "plus": "+",
+    "minus": "-",
+    "multiplied": "*",
+    "divided": "/",
+}
+
+WRONG_OPERATORS: list[str] = [
+    "plus?",
+    "minus?",
+    "multiplied?",
+    "divided?",
+    "plus plus",
+    "plus multiplied",
+    "minus multiplied",
+    "minus minus",
+    "multiplied multiplied",
+    "divided divided",
+    "What is?",
+]
+
+
+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.
+    """
+    _validate_errors(question)
+    result: int = 0
+    new_question: list[str] = _reformat(question)
+    # Reduce iteratively: evaluate the first three-token slice
+    # and fold the result left-to-right.
+    while new_question:
+        try:
+            if len(new_question) == 3:
+                _validate_evaluation_pattern(new_question)
+                return _math_operation(new_question)
+
+            if len(new_question) == 1:
+                return int(new_question[0])
+
+            _validate_evaluation_pattern(new_question[:3])
+            result = _math_operation(new_question[:3])
+            new_question = [str(result)] + new_question[3:]
+        except Exception as exc:
+            raise ValueError("syntax error") from exc
+
+
+def _math_operation(question: list[str]) -> int:
+    """
+    Compute a single binary arithmetic operation.
+
+    Expects a three-token slice like ``['3', '+', '4']`` and returns
+    the integer result. Division performs floor division (``//``) to
+    match exercise rules.
+
+    :param question: Three tokens ``[lhs, operator, rhs]``.
+    :type question: list[str]
+    :returns: The computed integer result.
+    :rtype: int
+    """
+    math_operator: str = question[1]
+    result: int = 0
+
+    if math_operator == "+":
+        result = int(question[0]) + int(question[-1])
+    elif math_operator == "-":
+        result = int(question[0]) - int(question[-1])
+    elif math_operator == "/":
+        result = int(question[0]) // int(question[-1])
+    elif math_operator == "*":
+        result = int(question[0]) * int(question[-1])
+
+    return result
+
+
+def _validate_evaluation_pattern(val: list) -> None:
+    """
+    Ensure a token slice matches expected evaluation patterns.
+
+    :param val: Token slice to validate, e.g.,
+                ['3', '+', '4'] or ['+', '4'] during reduction.
+    :type val: list
+    :raises ValueError: If the pattern is invalid (syntax error).
+    """
+    if len(val) == 3 and val[1] not in STR_TO_OPERATOR.values():
+        raise ValueError("syntax error")
+
+    if len(val) == 2 and val[0] not in STR_TO_OPERATOR.values():
+        raise ValueError("syntax error")
+
+
+def _reformat(question: str) -> list:
+    """
+    Tokenize a natural-language math question into numbers
+    and operator symbols.
+
+    :param question: Raw question string.
+    :type question: str
+    :returns: Token list with numbers and operator symbols.
+    :rtype: list[str]
+    """
+    # 1: Remove '?' mark
+    question = question.replace("?", "")
+    # 2: Convert all operators writen in word into proper math sign
+    question_list: list[str] = question.split()
+    formated_question_list: list[str] = []
+    for item in question_list:
+        if not (
+            item.isdigit()
+            or item in STR_TO_OPERATOR
+            or item in STR_TO_OPERATOR.values()
+            or any(val in item for val in STR_TO_OPERATOR.values())
+        ):
+            continue
+
+        if item in STR_TO_OPERATOR:
+            formated_question_list.append(STR_TO_OPERATOR[item])
+        elif item.isdigit():
+            formated_question_list.append(item)
+        elif item in STR_TO_OPERATOR.values():
+            formated_question_list.append(item)
+        elif any(val in item for val in STR_TO_OPERATOR.values()):
+            formated_question_list.append(item)
+
+    return formated_question_list
+
+
+def _validate_errors(question: str) -> None:
+    """
+    Pre-validate unsupported or malformed questions.
+
+    :param question: Raw question string.
+    :type question: str
+    :raises ValueError: Unknown operation or malformed
+                        phrasing (syntax error).
+    """
+    if "cubed" in question:
+        raise ValueError("unknown operation")
+
+    for item in WRONG_OPERATORS:
+        if item in question:
+            raise ValueError("syntax error")