# create a DataFrame of example data
data = pd.DataFrame(columns=['date'])
for i in range(30):
    this_date = start_date + timedelta(days=random.randint(0,days_diff))

    data = data.append({'date':this_date,'value': 'test'}, ignore_index=True)
# add columns for the week and year of the dates
data['date_week'] = data['date'].apply(lambda x: x.isocalendar()[1])
data['date_year'] = data['date'].apply(lambda x: x.isocalendar()[0])