REF: repr for Solver

docs/source/i_whatsnew.rst

@@ -42,6 +42,10 @@ email contact through **[email protected]**.
      - The ``__repr__`` method of *FXRates* and *FXForwards* types is changed for better
        display in associated packages.
        `(388) <https://github.com/attack68/rateslib/pull/388>`_
+   * - Refactor
+     - The ``__repr__`` method of *Solver* types is changed for better
+       display in associated packages.
+       `(389) <https://github.com/attack68/rateslib/pull/389>`_
    * - Performance
      - Improve the speed of bond :meth:`~rateslib.instruments.FixedRateBond.ytm` calculations from about 750us to
        500us on average.

python/rateslib/solver.py

@@ -1044,6 +1044,9 @@ def __init__(
         }
         self.iterate()
 
+    def __repr__(self):
+        return f"<rl.Solver:{self.id} at {hex(id(self))}>"
+
     def _parse_instrument(self, value):
         """
         Parses different input formats for an instrument given to the ``Solver``.

python/tests/test_solver.py

@@ -145,6 +145,33 @@ def test_basic_solver(algo) -> None:
         assert abs(float(curve.nodes[key]) - expected[i]) < 1e-6
 
 
+def test_solver_repr():
+    curve = Curve(
+        {
+            dt(2022, 1, 1): 1.0,
+            dt(2023, 1, 1): 1.0,
+            dt(2024, 1, 1): 1.0,
+            dt(2025, 1, 1): 1.0,
+        },
+        id="v",
+    )
+    instruments = [
+        (IRS(dt(2022, 1, 1), "1Y", "Q"), (curve,), {}),
+        (IRS(dt(2022, 1, 1), "2Y", "Q"), (curve,), {}),
+        (IRS(dt(2022, 1, 1), "3Y", "Q"), (curve,), {}),
+    ]
+    s = np.array([1.0, 1.6, 2.0])
+    solver = Solver(
+        curves=[curve],
+        instruments=instruments,
+        s=s,
+        id="S_ID"
+    )
+    result = solver.__repr__()
+    expected = f"<rl.Solver:S_ID at {hex(id(solver))}>"
+    assert result == expected
+
+
 @pytest.mark.parametrize("algo", ["gauss_newton", "levenberg_marquardt", "gradient_descent"])
 def test_solver_reiterate(algo) -> None:
     # test that curves are properly updated by a reiterate