custom_retail_primitive.py

def total_previous_month(numeric, datetime, time):
    """Return total of `numeric` column in the month prior to `time`."""
    df = pd.DataFrame({'value': numeric, 'time': datetime})
    previous_month = time.month - 1
   
    # Handle January
    if previous_month == 0:
        previous_month = 12
        previous_year = time.year - 1
        
        # Filter data
        df = df[(df['time'].dt.month == previous_month) & 
                (df['time'].dt.year == previous_year)]
        
    else:
        df = df[df['time'].dt.month == previous_month]
        
    # Sum up total
    total = df['value'].sum()
    
    return total
  
# Define the custom primitive
total_previous = make_agg_primitive(total_previous_month,
                                    input_types = [ft.variable_types.Numeric,
                                                   ft.variable_types.Datetime],
                                    return_type = ft.variable_types.Numeric, 
                                    uses_calc_time = True)