Python pandas: fill a dataframe row by row

Question

The simple task of adding a row to a pandas.DataFrame object seems to be hard to accomplish. There are 3 stackoverflow questions relating to this, none of which

Answer 1

This is a simpler version

import pandas as pd
df = pd.DataFrame(columns=('col1', 'col2', 'col3'))
for i in range(5):
   df.loc[i] = ['','','']`