code sample for pandas-dev#42878

Author: simonjayhawkins

bisect/42878.py

@@ -0,0 +1,17 @@
+# BUG: [float32 precision] pandas float32 mean is inconsistent with numpy #42878
+
+import numpy as np
+
+import pandas as pd
+
+print(pd.__version__)
+
+a = pd.Series(np.random.normal(scale=0.1, size=(1_000_000,)).astype(np.float32)).pow(2)
+
+result = np.mean(a)
+print(result, type(result))
+
+expected = np.mean(a.values)
+assert isinstance(result, np.float32)
+assert isinstance(expected, np.float32)
+assert result == expected