code: def find_key(self, regex):
          
          log = logging.getLogger(self.cls_logger + '.find_key')
          if not isinstance(regex, basestring):
              log.error('regex argument is not a string')
              return None
          log.info('Looking up a single S3 key based on regex: %s', regex)
          matched_keys = []
          for item in self.bucket.objects.all():
              log.debug('Checking if regex matches key: %s', item.key)
              match = re.search(regex, item.key)
              if match:
                  matched_keys.append(item.key)
          if len(matched_keys) == 1:
              log.info('Found matching key: %s', matched_keys[0])
              return matched_keys[0]
          elif len(matched_keys) > 1:
              log.info('Passed regex matched more than 1 key: %s', regex)
              return None
          else:
              log.info('Passed regex did not match any key: %s', regex)
              return None
docs: Attempts to find a single S3 key based on the passed regex
  
          Given a regular expression, this method searches the S3 bucket
          for a matching key, and returns it if exactly 1 key matches.
          Otherwise, None is returned.
  
          :param regex: (str) Regular expression for an S3 key
          :return: (str) Full length S3 key matching the regex, None
              otherwise