code: def to_datetime(date_key):
          '''
          Extract the first date from 'key' matching YYYY-MM-DD
          or YYYY-MM, and convert to datetime.
          '''
          match = re.search(r'\d{4}-\d{2}(-\d{2})?', date_key)
          formatter = '%Y-%m'
          if len(match.group()) == 10:
              formatter += '-%d'
          return datetime.strptime(
              match.group(), formatter).replace(tzinfo=pytz.UTCf to_datetime(date_key):
          '''
          Extract the first date from 'key' matching YYYY-MM-DD
          or YYYY-MM, and convert to datetime.
          '''
          match = re.search(r'\d{4}-\d{2}(-\d{2})?', date_key)
          formatter = '%Y-%m'
          if len(match.group()) == 10:
              formatter += '-%d'
          return datetime.strptime(
              match.group(), formatter).replace(tzinfo=pytz.UTC)
docs: Extract the first date from 'key' matching YYYY-MM-DD
          or YYYY-MM, and convert to datetime.