BUG: Explicit quantile to 0.5. Fix format #33200

Author: mabelvj

pandas/_libs/groupby.pyx

@@ -781,7 +781,7 @@ def group_quantile(ndarray[float64_t] out,
     if labels.any():
         # Put '-1' (NaN) labels as the last group so it does not interfere
         # with the calculations.
-        labels[labels==-1] = np.max(labels) + 1
+        labels[labels == -1] = np.max(labels) + 1
     # Get an index of values sorted by labels and then values
     order = (values, labels)
     sort_arr = np.lexsort(order).astype(np.int64, copy=False)

pandas/tests/groupby/test_function.py

@@ -1500,7 +1500,7 @@ def test_quantile_missing_group_values_correct_results(
     # GH 28662, GH 33200
     df = pd.DataFrame({"key": key, "val": val})
 
-    result = df.groupby("key").quantile()
+    result = df.groupby("key").quantile(0.5)
     expected = pd.DataFrame(
         expected_val, index=pd.Index(expected_key, name="key"), columns=["val"]
     )