code: def _find_script(script_name):
      
      if os.path.isfile(script_name):
          return script_name
      path = os.getenv('PATH', os.defpath).split(os.pathsep)
      for folder in path:
          if not folder:
              continue
          fn = os.path.join(folder, script_name)
          if os.path.isfile(fn):
              return fn
  
      sys.stderr.write('Could not find script {0}\n'.format(script_name))
      raise SystemExit(1)
docs: Find the script.
  
      If the input is not a file, then $PATH will be searched.