docs: def is_py_script(filename):
      "Returns True if a file is a python executable."
      if not os.path.exists(filename) and os.path.isfile(filename):
          return False
      elif filename.endswith(".py"):
          return True
      elif not os.access(filename, os.X_OK):
          return False
      else:
          try:
              with open(filename, "r") as fp:
                  first_line = fp.readline().strip()
              return "#!" in first_line and "python" in first_line
          except StopIteration:
              return False