# year/month/day,visitors,prospects

event_file = open('attendance.txt','r')
reportfile = open('report_by_year.txt','w')     # for the year-wise report

visitors  = 0
prospects = 0
num_lines = 0
year_str  = ''            # for processing the year
visitors_for_year = 0     # for processing the year

for event_str in event_file:
    num_lines += 1
    event_str = event_str.strip()
    date,visitors_str,prospects_str = event_str.split(',')
    visitors  += int(visitors_str)
    prospects += int(prospects_str)

    # process the year
    if year_str == '':
        year_str = date[0:4]
        visitors_for_year = 0
    elif year_str != date[0:4]:
        print('{} total visitors {:3d}'.format(year_str,visitors_for_year), \
              file=reportfile)
        year_str = date[0:4]
        visitors_for_year = 0
    visitors_for_year += int(visitors_str)

# print the final year
print('{} total visitors {:3d}'.format(year_str,visitors_for_year), \
      file=reportfile)

print()
print('Visitors  {:3d} average {:2.2f}'.format(visitors, visitors/num_lines))
print('Prospects {:3d} average {:2.2f}'.format(prospects, prospects/num_lines))

event_file.close()
reportfile.close()     # for the year-wise report