style: Fix ruff lint and format violations

- Replace ambiguous unicode multiplication sign with ASCII x
- Apply ruff format to long assert lines
- Fix test_linear4bit.py pre-existing format violation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: TimDettmers

tests/test_functional.py

@@ -1170,8 +1170,12 @@ def test_4bit_quant(self, device, dtype, quant_type, blocksize):
 
         err_mean, err_std = error_stats[quant_type]["err"][blocksize]
         relerr_mean, relerr_std = error_stats[quant_type]["rel_err"][blocksize]
-        assert err < err_mean + N_SIGMA * err_std, f"abs error {err:.6f} exceeds {err_mean:.6f} + {N_SIGMA}*{err_std:.6f}"
-        assert relerr < relerr_mean + N_SIGMA * relerr_std, f"rel error {relerr:.6f} exceeds {relerr_mean:.6f} + {N_SIGMA}*{relerr_std:.6f}"
+        assert err < err_mean + N_SIGMA * err_std, (
+            f"abs error {err:.6f} exceeds {err_mean:.6f} + {N_SIGMA}*{err_std:.6f}"
+        )
+        assert relerr < relerr_mean + N_SIGMA * relerr_std, (
+            f"rel error {relerr:.6f} exceeds {relerr_mean:.6f} + {N_SIGMA}*{relerr_std:.6f}"
+        )
 
     @pytest.mark.parametrize("device", get_available_devices())
     @pytest.mark.parametrize("quant_type", ["fp4", "nf4"])
@@ -1378,14 +1382,22 @@ def test_gemv_4bit(self, device, dim, dtype, storage_type, double_quant, kind):
         maxratio = relerr2 / relerr3
 
         # Expected (mean, std) for err1, relerr1, maxerr1 per dtype/dim group.
-        # Measured from 100 iterations × all storage_type/kind/DQ combos on RTX 4090.
+        # Measured from 100 iterations x all storage_type/kind/DQ combos on RTX 4090.
         # std is for individual iterations (not the average), so thresholds are generous
         # enough to accommodate GPU architecture differences (e.g., T4, XPU, Blackwell).
         N_SIGMA = 7
         gemv_thresholds = {
             torch.float16: {
-                "le512": {"err1": (0.000052, 0.0000063), "relerr1": (0.00024, 0.000357), "maxerr1": (0.00042, 0.0000687)},
-                "gt512": {"err1": (0.000018, 0.0000028), "relerr1": (0.00010, 0.000197), "maxerr1": (0.00017, 0.0000179)},
+                "le512": {
+                    "err1": (0.000052, 0.0000063),
+                    "relerr1": (0.00024, 0.000357),
+                    "maxerr1": (0.00042, 0.0000687),
+                },
+                "gt512": {
+                    "err1": (0.000018, 0.0000028),
+                    "relerr1": (0.00010, 0.000197),
+                    "maxerr1": (0.00017, 0.0000179),
+                },
             },
             torch.float32: {
                 "le512": {"err1": (2e-8, 2e-9), "relerr1": (8e-7, 1.2e-6), "maxerr1": (6e-8, 2e-8)},

tests/test_linear4bit.py

@@ -276,9 +276,7 @@ def test_quant_storage_shard_roundtrip(device, quant_type, quant_storage):
     reassembled = torch.cat(shards).reshape(qB.shape)
 
     assert reassembled.dtype == qB.dtype
-    assert torch.equal(
-        reassembled.view(torch.uint8), qB.view(torch.uint8)
-    ), "Bytes changed after shard roundtrip"
+    assert torch.equal(reassembled.view(torch.uint8), qB.view(torch.uint8)), "Bytes changed after shard roundtrip"
 
     out = bnb.functional.gemv_4bit(A, reassembled.t(), state=state)
     torch.testing.assert_close(out, ref)

tests/test_parametrize.py

@@ -88,8 +88,12 @@ def test_replace_parameter_4bit(device, dtype, quant_type, compress_statistics,
 
     abs_mean, abs_std = expected_errors[quant_type][blocksize]["abs"]
     rel_mean, rel_std = expected_errors[quant_type][blocksize]["rel"]
-    assert err_mean < abs_mean + N_SIGMA * abs_std, f"Mean abs error {err_mean:.6f} exceeds {abs_mean:.6f} + {N_SIGMA}*{abs_std:.6f}"
-    assert relerr < rel_mean + N_SIGMA * rel_std, f"Mean rel error {relerr:.6f} exceeds {rel_mean:.6f} + {N_SIGMA}*{rel_std:.6f}"
+    assert err_mean < abs_mean + N_SIGMA * abs_std, (
+        f"Mean abs error {err_mean:.6f} exceeds {abs_mean:.6f} + {N_SIGMA}*{abs_std:.6f}"
+    )
+    assert relerr < rel_mean + N_SIGMA * rel_std, (
+        f"Mean rel error {relerr:.6f} exceeds {rel_mean:.6f} + {N_SIGMA}*{rel_std:.6f}"
+    )
 
 
 @pytest.mark.parametrize("device", get_available_devices())
@@ -129,8 +133,12 @@ def __init__(self, device, dtype):
     abs_mean, abs_std = 0.072802, 0.000072
     rel_mean, rel_std = 0.203327, 0.000312
 
-    assert err_mean < abs_mean + N_SIGMA * abs_std, f"Mean abs error {err_mean:.6f} exceeds {abs_mean:.6f} + {N_SIGMA}*{abs_std:.6f}"
-    assert relerr < rel_mean + N_SIGMA * rel_std, f"Mean rel error {relerr:.6f} exceeds {rel_mean:.6f} + {N_SIGMA}*{rel_std:.6f}"
+    assert err_mean < abs_mean + N_SIGMA * abs_std, (
+        f"Mean abs error {err_mean:.6f} exceeds {abs_mean:.6f} + {N_SIGMA}*{abs_std:.6f}"
+    )
+    assert relerr < rel_mean + N_SIGMA * rel_std, (
+        f"Mean rel error {relerr:.6f} exceeds {rel_mean:.6f} + {N_SIGMA}*{rel_std:.6f}"
+    )
 
 
 @pytest.mark.parametrize("device", get_available_devices())
@@ -398,8 +406,12 @@ def test_parametrization_forward_method():
     N_SIGMA = 7
     abs_mean, abs_std = 0.072842, 0.001180
     rel_mean, rel_std = 0.202648, 0.004729
-    assert err_mean < abs_mean + N_SIGMA * abs_std, f"Mean abs error {err_mean:.6f} exceeds {abs_mean:.6f} + {N_SIGMA}*{abs_std:.6f}"
-    assert relerr < rel_mean + N_SIGMA * rel_std, f"Mean rel error {relerr:.6f} exceeds {rel_mean:.6f} + {N_SIGMA}*{rel_std:.6f}"
+    assert err_mean < abs_mean + N_SIGMA * abs_std, (
+        f"Mean abs error {err_mean:.6f} exceeds {abs_mean:.6f} + {N_SIGMA}*{abs_std:.6f}"
+    )
+    assert relerr < rel_mean + N_SIGMA * rel_std, (
+        f"Mean rel error {relerr:.6f} exceeds {rel_mean:.6f} + {N_SIGMA}*{rel_std:.6f}"
+    )
 
 
 @pytest.mark.parametrize("device", get_available_devices())