code: def get_file_named(self, fldr, xtn):
          
          res = []       # list of Sample objects
          for root, _, files in os.walk(fldr):
              for basename in files:
                  if fnmatch.fnmatch(basename, xtn):
                      filename = os.path.join(root, basename)
                      res.append(filename)
  
          if len(res) > 0:   
              return res[0]
          else:
              return None
docs: scans a directory for files like *.GZ or *.ZIP and returns
          the filename of the first one found (should only be one of
          each file here