Fix decimal.FloatOperation error in pytest.approx Decimal __repr__

changelog/13530.bugfix.rst

@@ -0,0 +1 @@
+Fixed a crash when using :func:`pytest.approx` and :class:`decimal.Decimal` instances with the :class:`decimal.FloatOperation` trap set.

src/_pytest/python_api.py

@@ -530,6 +530,26 @@ class ApproxDecimal(ApproxScalar):
     DEFAULT_ABSOLUTE_TOLERANCE = Decimal("1e-12")
     DEFAULT_RELATIVE_TOLERANCE = Decimal("1e-6")
 
+    def __repr__(self) -> str:
+        if isinstance(self.rel, float):
+            rel = Decimal.from_float(self.rel)
+        else:
+            rel = self.rel
+
+        if isinstance(self.abs, float):
+            abs_ = Decimal.from_float(self.abs)
+        else:
+            abs_ = self.abs
+
+        if rel is not None and Decimal("1e-3") <= rel <= Decimal("1e3"):
+            tol_str = f"{rel:.1e}"
+        elif abs_ is not None:
+            tol_str = f"{abs_:.1e}"
+        else:
+            tol_str = "???"
+
+        return f"{self.expected} ± {tol_str}"
+
 
 def approx(expected, rel=None, abs=None, nan_ok: bool = False) -> ApproxBase:
     """Assert that two numbers (or two ordered sequences of numbers) are equal to each other

testing/python/approx.py

@@ -1015,6 +1015,11 @@ def __len__(self):
         expected_repr = "approx([1 ± 1.0e-06, 2 ± 2.0e-06, 3 ± 3.0e-06, 4 ± 4.0e-06])"
         assert repr(approx(expected)) == expected_repr
 
+    def test_decimal_approx_repr(self, monkeypatch) -> None:
+        monkeypatch.setitem(decimal.getcontext().traps, decimal.FloatOperation, True)
+        approx_obj = pytest.approx(decimal.Decimal("2.60"))
+        assert decimal.Decimal("2.600001") == approx_obj
+
     def test_allow_ordered_sequences_only(self) -> None:
         """pytest.approx() should raise an error on unordered sequences (#9692)."""
         with pytest.raises(TypeError, match="only supports ordered sequences"):