pandas. dataframe selects methods by row index expression

The list expression and dataframe.iloc are used to split a data set that is read from the csv file by equidistant sampling

Sir Into an indexed list:

index_list = ['%d' %i for i in range(df.shape[0]) if i % 3 == 0]

Select in dataframe

sample_df = df.iloc[index_list]

A combined

sample_df = df.iloc[['%d' %i for i in range(df.shape[0]) if i % 3 == 0]]

Do you have a better way? Your comments are welcome.