Python more functions

Question

I would like to separate this into several smaller functions in order to make it look tidier and easier to read, but whenever I try this I cannot seem to get it to work. Any help would be appreciated.

At the moment my code looks like this

def print_monthly_totals (input_csv_filename):
    data = open(input_csv_filename).readlines()
    print('Rainfall totals for each month')
    for line in data:
        columns = line.split(',')
        month = int(columns[0])
        num_days = int(columns[1])
        total_rainfall = 0
        for col in columns[2 : 2 + num_days]:
            total_rainfall += float(col)

        print('Month {:2}: {:.1f}'.format(month, total_rainfall))

I would like it to look more like the example below

def print_monthly_totals (input_csv_filename):
    data = open(input_csv_filename).readlines()
    print('Rainfall totals for each month')
def SOMETHING(SOMETHING):    #The SOMETHING is just a filler
    for line in data:
        columns = line.split(',')
        month = int(columns[0])
        num_days = int(columns[1])
        total_rainfall = 0
def SOMETHING(SOMETHING):    #The SOMETHING is just a filler
        for col in columns[2 : 2 + num_days]:
            total_rainfall += float(col)

        print('Month {:2}: {:.1f}'.format(month, total_rainfall))

Answer 1

You could shorten up your function like this:

def print_monthly_totals (input_csv_filename):
    data = open(input_csv_filename).readlines()
    print('Rainfall totals for each month')
    for line in data:
        columns = line.split(',')
        month, num_days = int(columns[0]), int(columns[1])
        daily_rainfalls = [float(x) for x in columns[2:2+num_days]]
        total_rainfall = sum(daily_rainfalls)

        print('Month {:2}: {:.1f}'.format(month, total_rainfall))

Or split it up into two functions like this:

def line_to_rainfall(line):
    cols = line.split(",")
    month, num_days = int(cols[0]), int(cols[1])
    daily_rainfalls = [float(x) for x in cols[2:2+num_days]]
    return month, daily_rainfalls


def print_monthly_totals (input_csv_filename):
    data = open(input_csv_filename).readlines()
    print('Rainfall totals for each month')
    for line in data:
        month, daily_rainfalls = line_to_rainfall(line)
        total_rainfall = sum(daily_rainfalls)
        print('Month {:2}: {:.1f}'.format(month, total_rainfall))

Answer 2

The most sensible split I can think of for this function separates the data-reading logic from the printing logic:

def print_monthly_totals (input_csv_filename):
    months, rainfall_totals = get_rainfall_data(input_csv_filename)

    print('Rainfall totals for each month')
    for month, total_rainfall in zip(months, rainfall_totals):
        print('Month {:2}: {:.1f}'.format(month, total_rainfall))

def get_rainfall_data(input_csv_filename):
    data = open(input_csv_filename) # .readlines() isn't necessary
    months = []
    rainfall_totals = []
    for line in data:
        columns = line.split(',')
        month = int(columns[0])
        months.append(month)
        num_days = int(columns[1])
        total_rainfall = 0
        for col in columns[2 : 2 + num_days]:
            total_rainfall += float(col)
        rainfall_totals.append(total_rainfall)
    return months, rainfall_totals