df.append() is not appending to the DataFrame
DataFrame.append is not an in-place operation. From the docs,
DataFrame.append(other, ignore_index=False, verify_integrity=False, sort=None)Append rows of other to the end of this frame, returning a new object.Columns not in this frame are added as new columns.
You need to assign the result back.
df8 = df8.append([s] * 2, ignore_index=True)df8 A B C D0 value aa value bb value cc value dd1 value aa value bb value cc value dd