code: def grep(self, regex):
          
          matches = []
          logger.debug("Searching student files for '{0}'".format(regex))
          for fname in self.student_files:
              if os.path.isfile(self.working_dir + fname):
                  for line in open(self.working_dir + fname, 'br'):
                      if re.search(regex.encode(), line):
                          logger.debug("{0} contains '{1}'".format(fname, regex))
                          matches.append(fname)
          return matches
docs: Scans the student files for text patterns.
  
          Args:
              regex (str):       Regular expression used for scanning inside the files.
  
          Returns:
              tuple:     Names of the matching files in the working directory.