py-05-calc

# Arithmetic Expression Evaluator

Implement a file **`solution.py`** containing a function:

```python
def evaluate(expr: str) -> float:
    ...
```

Evaluate an arithmetic expression given as a string and return its value as a
`float`.

Supported syntax:

- Binary operators `+`, `-`, `*`, `/` with standard precedence
  (`*` and `/` bind tighter than `+` and `-`) and left-to-right associativity.
- Parentheses `(` ... `)` for grouping.
- Unary plus and minus, e.g. `-3`, `-(2 + 1)`, `2 * -3`.
- Integer and float literals, e.g. `42`, `3.14`, `.5`, `10.`.
- Arbitrary surrounding / internal whitespace, which is ignored.

Requirements:

- Return the numeric result as a `float`. For example
  `evaluate("1 + 2 * 3") == 7.0` and `evaluate("(1 + 2) * 3") == 9.0`.
- Implement a real parser/evaluator that respects precedence and parentheses.
  **Do not** use `eval`, `exec`, or similar (the harness may inspect for this).
- Raise `ValueError` on malformed input. Malformed includes: empty / whitespace-only
  input, unbalanced parentheses, a missing operand or operator (e.g. `"1 +"`,
  `"1 2"`, `"* 3"`), and unexpected characters.
- Division by zero should raise an error (a `ZeroDivisionError` or `ValueError`
  is acceptable).

Examples:

```python
evaluate("2 + 3 * 4")      # 14.0
evaluate("(2 + 3) * 4")    # 20.0
evaluate("10 / 4")         # 2.5
evaluate("-3 + 2")         # -1.0
evaluate("2 * (1 + -1.5)") # -1.0
```

import pytest

from solution import evaluate


def test_simple_addition():
    assert evaluate("1 + 2") == 3.0


def test_precedence():
    assert evaluate("2 + 3 * 4") == 14.0
    assert evaluate("1 + 2 * 3") == 7.0


def test_parentheses_override_precedence():
    assert evaluate("(2 + 3) * 4") == 20.0
    assert evaluate("(1 + 2) * 3") == 9.0


def test_division_is_float():
    assert evaluate("10 / 4") == 2.5
    assert isinstance(evaluate("4 / 2"), float)


def test_unary_minus():
    assert evaluate("-3 + 2") == -1.0
    assert evaluate("2 * -3") == -6.0
    assert evaluate("-(2 + 1)") == -3.0


def test_float_and_whitespace():
    assert evaluate("  3.14 + .86 ") == pytest.approx(4.0)
    assert evaluate("10. / 4") == 2.5


def test_left_associativity():
    assert evaluate("10 - 2 - 3") == 5.0
    assert evaluate("100 / 5 / 2") == 10.0


def test_nested_parens():
    assert evaluate("2 * (1 + (3 - 1) * 2)") == 10.0


def test_malformed_raises_value_error():
    for bad in ["", "   ", "1 +", "* 3", "1 2", "(1 + 2", "1 + 2)", "1 + * 2", "3 $ 4"]:
        with pytest.raises(ValueError):
            evaluate(bad)


def test_division_by_zero_raises():
    with pytest.raises((ValueError, ZeroDivisionError)):
        evaluate("1 / 0")

You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.

```python
def evaluate(expr: str) -> float:
    import re

    # Remove all whitespace
    expr = expr.replace(' ', '')

    # Check for empty or whitespace-only input
    if not expr:
        raise ValueError("Empty input")

    # Tokenize the expression
    tokens = []
    i = 0
    n = len(expr)
    while i < n:
        c = expr[i]
        if c in '()+-*/':
            tokens.append(c)
            i += 1
        elif c.isdigit() or c == '.':
            j = i
            has_decimal = False
            while j < n and (expr[j].isdigit() or expr[j] == '.'):
                if expr[j] == '.':
                    if has_decimal:
                        raise ValueError("Invalid number format")
                    has_decimal = True
                j += 1
            num_str = expr[i:j]
            # Handle cases like '.5' or '10.'
            if num_str.startswith('.') and len(num_str) == 1:
                num_str = '0' + num_str
            if num_str.endswith('.') and len(num_str) > 1:
                num_str = num_str[:-1]
            tokens.append(num_str)
            i = j
        else:
            raise ValueError(f"Unexpected character: {c}")

    # Check for empty tokens or invalid sequences
    if not tokens:
        raise ValueError("Empty input")

    # Handle unary operators
    processed_tokens = []
    i = 0
    n = len(tokens)
    while i < n:
        token = tokens[i]
        if token in '+-':
            if i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/':
                # It's a unary operator
                processed_tokens.append(token)
                i += 1
            else:
                processed_tokens.append(token)
                i += 1
        else:
            processed_tokens.append(token)
            i += 1

    tokens = processed_tokens

    # Convert number tokens to floats
    for i, token in enumerate(tokens):
        if token not in '+-*/()':
            try:
                tokens[i] = float(token)
            except ValueError:
                raise ValueError(f"Invalid number: {token}")

    # Evaluate the expression using two stacks
    values = []
    ops = []
    i = 0
    n = len(tokens)

    while i < n:
        token = tokens[i]
        if isinstance(token, float):
            values.append(token)
        elif token == '(':
            ops.append(token)
        elif token == ')':
            if not ops:
                raise ValueError("Mismatched parentheses")
            while ops and ops[-1] != '(':
                apply_operator(ops, values)
            if not ops:
                raise ValueError("Mismatched parentheses")
            ops.pop()  # Remove the '('
        else:
            while ops and ops[-1] != '(' and precedence(ops[-1]) >= precedence(token):
                apply_operator(ops, values)
            ops.append(token)
        i += 1

    while ops:
        if ops[-1] == '(':
            raise ValueError("Mismatched parentheses")
        apply_operator(ops, values)

    if len(values) != 1:
        raise ValueError("Invalid expression")

    return values[0]

def precedence(op):
    if op in '*/':
        return 2
    elif op in '+-':
        return 1
    return 0

def apply_operator(ops, values):
    op = ops.pop()
    if len(values) < 2:
        raise ValueError("Missing operand")
    b = values.pop()
    a = values.pop()
    if op == '+':
        values.append(a + b)
    elif op == '-':
        values.append(a - b)
    elif op == '*':
        values.append(a * b)
    elif op == '/':
        if b == 0:
            raise ZeroDivisionError("Division by zero")
        values.append(a / b)
```

[
  {
    "total": 10,
    "answer": "```python\ndef evaluate(expr: str) -> float:\n    import re\n\n    # Remove all whitespace\n    expr = expr.replace(' ', '')\n\n    # Check for empty or whitespace-only input\n    if not expr:\n        raise ValueError(\"Empty input\")\n\n    # Tokenize the expression\n    tokens = []\n    i = 0\n    n = len(expr)\n    while i < n:\n        c = expr[i]\n        if c in '()+-*/':\n            tokens.append(c)\n            i += 1\n        elif c.isdigit() or c == '.':\n            j = i\n            has_decimal = False\n            while j < n and (expr[j].isdigit() or expr[j] == '.'):\n                if expr[j] == '.':\n                    if has_decimal:\n                        raise ValueError(\"Invalid number format\")\n                    has_decimal = True\n                j += 1\n            num_str = expr[i:j]\n            # Handle cases like '.5' or '10.'\n            if num_str.startswith('.') and len(num_str) == 1:\n                num_str = '0' + num_str\n            if num_str.endswith('.') and len(num_str) > 1:\n                num_str = num_str[:-1]\n            tokens.append(num_str)\n            i = j\n        else:\n            raise ValueError(f\"Unexpected character: {c}\")\n\n    # Check for empty tokens or invalid sequences\n    if not tokens:\n        raise ValueError(\"Empty input\")\n\n    # Handle unary operators\n    processed_tokens = []\n    i = 0\n    n = len(tokens)\n    while i < n:\n        token = tokens[i]\n        if token in '+-':\n            if i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/':\n                # It's a unary operator\n                processed_tokens.append(token)\n                i += 1\n            else:\n                processed_tokens.append(token)\n                i += 1\n        else:\n            processed_tokens.append(token)\n            i += 1\n\n    tokens = processed_tokens\n\n    # Convert number tokens to floats\n    for i, token in enumerate(tokens):\n        if token not in '+-*/()':\n            try:\n                tokens[i] = float(token)\n            except ValueError:\n                raise ValueError(f\"Invalid number: {token}\")\n\n    # Evaluate the expression using two stacks\n    values = []\n    ops = []\n    i = 0\n    n = len(tokens)\n\n    while i < n:\n        token = tokens[i]\n        if isinstance(token, float):\n            values.append(token)\n        elif token == '(':\n            ops.append(token)\n        elif token == ')':\n            if not ops:\n                raise ValueError(\"Mismatched parentheses\")\n            while ops and ops[-1] != '(':\n                apply_operator(ops, values)\n            if not ops:\n                raise ValueError(\"Mismatched parentheses\")\n            ops.pop()  # Remove the '('\n        else:\n            while ops and ops[-1] != '(' and precedence(ops[-1]) >= precedence(token):\n                apply_operator(ops, values)\n            ops.append(token)\n        i += 1\n\n    while ops:\n        if ops[-1] == '(':\n            raise ValueError(\"Mismatched parentheses\")\n        apply_operator(ops, values)\n\n    if len(values) != 1:\n        raise ValueError(\"Invalid expression\")\n\n    return values[0]\n\ndef precedence(op):\n    if op in '*/':\n        return 2\n    elif op in '+-':\n        return 1\n    return 0\n\ndef apply_operator(ops, values):\n    op = ops.pop()\n    if len(values) < 2:\n        raise ValueError(\"Missing operand\")\n    b = values.pop()\n    a = values.pop()\n    if op == '+':\n        values.append(a + b)\n    elif op == '-':\n        values.append(a - b)\n    elif op == '*':\n        values.append(a * b)\n    elif op == '/':\n        if b == 0:\n            raise ZeroDivisionError(\"Division by zero\")\n        values.append(a / b)\n```",
    "passed": 8,
    "test_error": "....F...F.                                                               [100%]\n=================================== FAILURES ===================================\n_______________________________ test_unary_minus _______________________________\n\n    def test_unary_minus():\n>       assert evaluate(\"-3 + 2\") == -1.0\n               ^^^^^^^^^^^^^^^^^^\n\ntest_calc.py:26: \n_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ \nsolution.py:94: in evaluate\n    apply_operator(ops, values)\n_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ \n\nops = [], values = [3.0]\n\n    def apply_operator(ops, values):\n        op = ops.pop()\n        if len(values) < 2:\n>           raise ValueError(\"Missing operand\")\nE           ValueError: Missing operand\n\nsolution.py:118: ValueError\n______________________ test_malformed_raises_value_error _______________________\n\n    def test_malformed_raises_value_error():\n        for bad in [\"\", \"   \", \"1 +\", \"* 3\", \"1 2\", \"(1 + 2\", \"1 + 2)\", \"1 + * 2\", \"3 $ 4\"]:\n>           with pytest.raises(ValueError):\n                 ^^^^^^^^^^^^^^^^^^^^^^^^^\nE           Failed: DID NOT RAISE ValueError\n\ntest_calc.py:47: Failed\n=========================== short test summary info ============================\nFAILED test_calc.py::test_unary_minus - ValueError: Missing operand\nFAILED test_calc.py::test_malformed_raises_value_error - Failed: DID NOT RAIS...\n2 failed, 8 passed in 0.03s"
  },
  {
    "total": 10,
    "answer": "```python\ndef evaluate(expr: str) -> float:\n    import re\n\n    # Remove all whitespace\n    expr = expr.replace(' ', '')\n\n    # Check for empty or whitespace-only input\n    if not expr:\n        raise ValueError(\"Empty input\")\n\n    # Tokenize the expression\n    tokens = []\n    i = 0\n    n = len(expr)\n    while i < n:\n        c = expr[i]\n        if c in '()+-*/':\n            tokens.append(c)\n            i += 1\n        elif c.isdigit() or c == '.':\n            j = i\n            has_decimal = False\n            while j < n and (expr[j].isdigit() or expr[j] == '.'):\n                if expr[j] == '.':\n                    if has_decimal:\n                        raise ValueError(\"Invalid number format\")\n                    has_decimal = True\n                j += 1\n            num_str = expr[i:j]\n            # Handle cases like '.5' or '10.'\n            if num_str.startswith('.') and len(num_str) == 1:\n                num_str = '0' + num_str\n            if num_str.endswith('.') and len(num_str) > 1:\n                num_str = num_str[:-1]\n            tokens.append(num_str)\n            i = j\n        else:\n            raise ValueError(f\"Unexpected character: {c}\")\n\n    # Check for empty tokens or invalid sequences\n    if not tokens:\n        raise ValueError(\"Empty input\")\n\n    # Handle unary operators\n    processed_tokens = []\n    i = 0\n    n = len(tokens)\n    while i < n:\n        token = tokens[i]\n        if token in '+-':\n            if i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/':\n                # It's a unary operator, push 0 before it\n                processed_tokens.append('0')\n            processed_tokens.append(token)\n            i += 1\n        else:\n            processed_tokens.append(token)\n            i += 1\n\n    tokens = processed_tokens\n\n    # Convert number tokens to floats\n    for i, token in enumerate(tokens):\n        if token not in '+-*/()':\n            try:\n                tokens[i] = float(token)\n            except ValueError:\n                raise ValueError(f\"Invalid number: {token}\")\n\n    # Evaluate the expression using two stacks\n    values = []\n    ops = []\n    i = 0\n    n = len(tokens)\n\n    while i < n:\n        token = tokens[i]\n        if isinstance(token, float):\n            values.append(token)\n        elif token == '(':\n            ops.append(token)\n        elif token == ')':\n            if not ops:\n                raise ValueError(\"Mismatched parentheses\")\n            while ops and ops[-1] != '(':\n                apply_operator(ops, values)\n            if not ops:\n                raise ValueError(\"Mismatched parentheses\")\n            ops.pop()  # Remove the '('\n        else:\n            while ops and ops[-1] != '(' and precedence(ops[-1]) >= precedence(token):\n                apply_operator(ops, values)\n            ops.append(token)\n        i += 1\n\n    while ops:\n        if ops[-1] == '(':\n            raise ValueError(\"Mismatched parentheses\")\n        apply_operator(ops, values)\n\n    if len(values) != 1:\n        raise ValueError(\"Invalid expression\")\n\n    return values[0]\n\ndef precedence(op):\n    if op in '*/':\n        return 2\n    elif op in '+-':\n        return 1\n    return 0\n\ndef apply_operator(ops, values):\n    op = ops.pop()\n    if len(values) < 2:\n        raise ValueError(\"Missing operand\")\n    b = values.pop()\n    a = values.pop()\n    if op == '+':\n        values.append(a + b)\n    elif op == '-':\n        values.append(a - b)\n    elif op == '*':\n        values.append(a * b)\n    elif op == '/':\n        if b == 0:\n            raise ZeroDivisionError(\"Division by zero\")\n        values.append(a / b)\n```",
    "passed": 8,
    "test_error": "....F...F.                                                               [100%]\n=================================== FAILURES ===================================\n_______________________________ test_unary_minus _______________________________\n\n    def test_unary_minus():\n        assert evaluate(\"-3 + 2\") == -1.0\n>       assert evaluate(\"2 * -3\") == -6.0\nE       AssertionError: assert -3.0 == -6.0\nE        +  where -3.0 = evaluate('2 * -3')\n\ntest_calc.py:27: AssertionError\n______________________ test_malformed_raises_value_error _______________________\n\n    def test_malformed_raises_value_error():\n        for bad in [\"\", \"   \", \"1 +\", \"* 3\", \"1 2\", \"(1 + 2\", \"1 + 2)\", \"1 + * 2\", \"3 $ 4\"]:\n>           with pytest.raises(ValueError):\n                 ^^^^^^^^^^^^^^^^^^^^^^^^^\nE           Failed: DID NOT RAISE ValueError\n\ntest_calc.py:47: Failed\n=========================== short test summary info ============================\nFAILED test_calc.py::test_unary_minus - AssertionError: assert -3.0 == -6.0\nFAILED test_calc.py::test_malformed_raises_value_error - Failed: DID NOT RAIS...\n2 failed, 8 passed in 0.02s"
  },
  {
    "total": 10,
    "answer": "```python\ndef evaluate(expr: str) -> float:\n    import re\n\n    # Remove all whitespace\n    expr = expr.replace(' ', '')\n\n    # Check for empty or whitespace-only input\n    if not expr:\n        raise ValueError(\"Empty input\")\n\n    # Tokenize the expression\n    tokens = []\n    i = 0\n    n = len(expr)\n    while i < n:\n        c = expr[i]\n        if c in '()+-*/':\n            tokens.append(c)\n            i += 1\n        elif c.isdigit() or c == '.':\n            j = i\n            has_decimal = False\n            while j < n and (expr[j].isdigit() or expr[j] == '.'):\n                if expr[j] == '.':\n                    if has_decimal:\n                        raise ValueError(\"Invalid number format\")\n                    has_decimal = True\n                j += 1\n            num_str = expr[i:j]\n            # Handle cases like '.5' or '10.'\n            if num_str.startswith('.') and len(num_str) == 1:\n                num_str = '0' + num_str\n            if num_str.endswith('.') and len(num_str) > 1:\n                num_str = num_str[:-1]\n            tokens.append(num_str)\n            i = j\n        else:\n            raise ValueError(f\"Unexpected character: {c}\")\n\n    # Check for empty tokens or invalid sequences\n    if not tokens:\n        raise ValueError(\"Empty input\")\n\n    # Handle unary operators\n    processed_tokens = []\n    i = 0\n    n = len(tokens)\n    while i < n:\n        token = tokens[i]\n        if token in '+-':\n            if i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/':\n                # It's a unary operator, push 0 before it\n                processed_tokens.append('0')\n                processed_tokens.append(token)\n                i += 1\n            else:\n                processed_tokens.append(token)\n                i += 1\n        else:\n            processed_tokens.append(token)\n            i += 1\n\n    tokens = processed_tokens\n\n    # Convert number tokens to floats\n    for i, token in enumerate(tokens):\n        if token not in '+-*/()':\n            try:\n                tokens[i] = float(token)\n            except ValueError:\n                raise ValueError(f\"Invalid number: {token}\")\n\n    # Evaluate the expression using two stacks\n    values = []\n    ops = []\n    i = 0\n    n = len(tokens)\n\n    while i < n:\n        token = tokens[i]\n        if isinstance(token, float):\n            values.append(token)\n        elif token == '(':\n            ops.append(token)\n        elif token == ')':\n            if not ops:\n                raise ValueError(\"Mismatched parentheses\")\n            while ops and ops[-1] != '(':\n                apply_operator(ops, values)\n            if not ops:\n                raise ValueError(\"Mismatched parentheses\")\n            ops.pop()  # Remove the '('\n        else:\n            while ops and ops[-1] != '(' and precedence(ops[-1]) >= precedence(token):\n                apply_operator(ops, values)\n            ops.append(token)\n        i += 1\n\n    while ops:\n        if ops[-1] == '(':\n            raise ValueError(\"Mismatched parentheses\")\n        apply_operator(ops, values)\n\n    if len(values) != 1:\n        raise ValueError(\"Invalid expression\")\n\n    return values[0]\n\ndef precedence(op):\n    if op in '*/':\n        return 2\n    elif op in '+-':\n        return 1\n    return 0\n\ndef apply_operator(ops, values):\n    op = ops.pop()\n    if len(values) < 2:\n        raise ValueError(\"Missing operand\")\n    b = values.pop()\n    a = values.pop()\n    if op == '+':\n        values.append(a + b)\n    elif op == '-':\n        values.append(a - b)\n    elif op == '*':\n        values.append(a * b)\n    elif op == '/':\n        if b == 0:\n            raise ZeroDivisionError(\"Division by zero\")\n        values.append(a / b)\n```",
    "passed": 8,
    "test_error": ""
  }
]