How to check if a date entry has been filled in a .csv file in Python

I have a simple web scraping python script that writes results to a .csv file. The script runs each day when I do a particular task (it's attached to another automation process) that I usually do daily. However sometimes I end up triggering it more than once per day, leaving me with additional entries. I only want to add an entry if the .csv file does not contain today's date. At the moment I have this, but it's causing the writer not to write at all.

with open('results.csv', mode='a') as csv_file:
    write = True
    for line in csv_file:
      if line.contains(date.today()):
          write = False
    if write == True:
        writer = csv.writer(csv_file, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)
        writer.writerow([date.today(),mainstream_count,specialist_count])

I'm sure I'm missing something simple here. Any help would be much appreciated.

Thanks, James.