Expression evaluator (no eval)

qwen3-30b-a3b: timed out

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.

from pathlib import Path from calc import evaluate  def test_precedence():    assert evaluate("2+3*4") == 14  def test_parentheses():    assert evaluate("(2+3)*4") == 20    assert evaluate("2*(3+(4-1))") == 12  def test_true_division():    assert evaluate("10/4") == 2.5  def test_left_associativity():    assert evaluate("10-3-2") == 5    assert evaluate("16/4/2") == 2  def test_unary_minus():    assert evaluate("-3+5") == 2    assert evaluate("2*-3") == -6  def test_whitespace_and_decimals():    assert evaluate("  1.5 + 2.25 ") == 3.75  def test_does_not_use_eval():    src = Path("calc.py").read_text()    assert "eval(" not in src    assert "exec(" not in src

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