Expression evaluator (no eval)

You are completing a coding task in one shot. Write complete files that satisfy the spec below. Tests (pytest) will be run against your files; you cannot run them yourself.

Reply with ONE JSON object and nothing else:
{"files": {"<relative path>": "<complete file content>", ...}}

Required deliverable files: calc.py

SPEC:
Create calc.py with exactly one public function:

evaluate(expr: str) -> float
    Evaluate an arithmetic expression containing numbers (integers or decimals), the binary operators + - * /, unary minus, parentheses, and arbitrary whitespace. Normal precedence: * and / bind tighter than + and -; operators of equal precedence associate left to right. Division is true division. Examples: evaluate("2+3*4") == 14, evaluate("(2+3)*4") == 20, evaluate("2*-3") == -6.

You must parse the expression yourself: using eval() or exec() is forbidden and is checked by the test suite. Use only the Python standard library.

```json
{
  "files": {
    "calc.py": "def evaluate(expr: str) -> float:\n    # Split the expression into tokens\n    tokens = expr.replace(' ', '').split()\n\n    # Define a helper function to evaluate an operator\n    def apply_operator(operators, values):\n        operator = operators.pop()\n        right = values.pop()\n        left = values.pop()\n        if operator == '+':\n            values.append(left + right)\n        elif operator == '-':\n            values.append(left - right)\n        elif operator == '*':\n            values.append(left * right)\n        elif operator == '/':\n            values.append(left / right)\n\n    # Define a helper function to evaluate an expression with parentheses\n    def evaluate_parentheses(tokens):\n        operators = []\n        values = []\n        i = 0\n        while i < len(tokens):\n            if tokens[i] == '(':\n                j = i + 1\n                balance = 1\n                while balance > 0:\n                    if tokens[j] == '(':\n                        balance += 1\n                    elif tokens[j] == ')':\n                        balance -= 1\n                    j += 1\n                values.append(evaluate_parentheses(tokens[i+1:j-1]))\n                i = j - 1\n            elif tokens[i].isdigit() or (tokens[i][0] == '-' and tokens[i][1:].isdigit()):\n                num = float(tokens[i])\n                while i + 1 < len(tokens) and tokens[i+1].isdigit():\n                    num = num * 10 + float(tokens[i+1])\n                    i += 1\n                values.append(num)\n            elif tokens[i] in '+-*/':\n                while (operators and operators[-1] != '(' and\n                       ((tokens[i] == '*' or tokens[i] == '/') and\n                        (operators[-1] == '+' or operators[-1] == '-'))):\n                    apply_operator(operators, values)\n                operators.append(tokens[i])\n            i += 1\n        while operators:\n            apply_operator(operators, values)\n        return values[0]\n\n    # Evaluate the expression\n    return evaluate_parentheses(tokens)"
  }
}
```

FFFFFF.                                                                  [100%]
=================================== FAILURES ===================================
_______________________________ test_precedence ________________________________
test_calc.py:7: in test_precedence
    assert evaluate("2+3*4") == 14
           ^^^^^^^^^^^^^^^^^
calc.py:54: in evaluate
    return evaluate_parentheses(tokens)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
calc.py:51: in evaluate_parentheses
    return values[0]
           ^^^^^^^^^
E   IndexError: list index out of range
_______________________________ test_parentheses _______________________________
test_calc.py:11: in test_parentheses
    assert evaluate("(2+3)*4") == 20
           ^^^^^^^^^^^^^^^^^^^
calc.py:54: in evaluate
    return evaluate_parentheses(tokens)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
calc.py:51: in evaluate_parentheses
    return values[0]
           ^^^^^^^^^
E   IndexError: list index out of range
______________________________ test_true_division ______________________________
test_calc.py:16: in test_true_division
    assert evaluate("10/4") == 2.5
           ^^^^^^^^^^^^^^^^
calc.py:54: in evaluate
    return evaluate_parentheses(tokens)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
calc.py:51: in evaluate_parentheses
    return values[0]
           ^^^^^^^^^
E   IndexError: list index out of range
___________________________ test_left_associativity ____________________________
test_calc.py:20: in test_left_associativity
    assert evaluate("10-3-2") == 5
           ^^^^^^^^^^^^^^^^^^
calc.py:54: in evaluate
    return evaluate_parentheses(tokens)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
calc.py:51: in evaluate_parentheses
    return values[0]
           ^^^^^^^^^
E   IndexError: list index out of range
_______________________________ test_unary_minus _______________________________
test_calc.py:25: in test_unary_minus
    assert evaluate("-3+5") == 2
           ^^^^^^^^^^^^^^^^
calc.py:54: in evaluate
    return evaluate_parentheses(tokens)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
calc.py:51: in evaluate_parentheses
    return values[0]
           ^^^^^^^^^
E   IndexError: list index out of range
_________________________ test_whitespace_and_decimals _________________________
test_calc.py:30: in test_whitespace_and_decimals
    assert evaluate("  1.5 + 2.25 ") == 3.75
           ^^^^^^^^^^^^^^^^^^^^^^^^^
calc.py:54: in evaluate
    return evaluate_parentheses(tokens)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
calc.py:51: in evaluate_parentheses
    return values[0]
           ^^^^^^^^^
E   IndexError: list index out of range
=========================== short test summary info ============================
FAILED test_calc.py::test_precedence - IndexError: list index out of range
FAILED test_calc.py::test_parentheses - IndexError: list index out of range
FAILED test_calc.py::test_true_division - IndexError: list index out of range
FAILED test_calc.py::test_left_associativity - IndexError: list index out of ...
FAILED test_calc.py::test_unary_minus - IndexError: list index out of range
FAILED test_calc.py::test_whitespace_and_decimals - IndexError: list index ou...
6 failed, 1 passed in 0.02s