new_contents: # take a file with dates and convert to # of days from the start instead
  
  import csv
  import datetime as dt
  
  # replace dates with increments of days
  with open("output.csv", "w") as output:
    writer = csv.writer(output)
    with open("input.csv") as inp:
      reader = csv.reader(inp)
      firstDay = None
      rowCount = 0
      dateFormat = "%Y-%m-%d"
      for row in reader:
        if rowCount > 0:
          date = row.pop()
          day = dt.datetime.strptime(date, dateFormat)
          if rowCount == 1:
            firstDay = day
          dayNum = (day - firstDay).days
          duration = "<[" + str(dayNum) + ", " + str(dayNum + 1) + "]>"
          row.append(duration)
  
        writer.writerow(row)
        rowCount += 1
  
subject: add python convert from date script