Python to add 7-day rolling sum to a CSV

7daysum.py

#!/usr/bin/python

import datetime
import sys

# Adds a 7-day rolling sum to a CSV
# Input: date,cases
# date format: yyyy-mm-dd
# Output: date,cases,last7days

recs = []
for rec in sys.stdin:
  rec = rec.strip().split(",")
  if len(rec) == 0:
    continue
  assert len(rec) == 2
  date = datetime.datetime.strptime(rec[0], '%Y-%m-%d')
  count = int(rec[1])
  recs.append((rec[0], date, count))

def last_7_days(end):
  start = end - datetime.timedelta(6)
  return sum(rec[2] for rec in recs if rec[1] <= end and rec[1] >= start)

for rec in recs:
  print ",".join([rec[0], str(rec[2]), str(last_7_days(rec[1]))])