code: def ensure_timestamp(func, argname, arg):
      
      try:
          return pd.Timestamp(arg)
      except ValueError as e:
          raise TypeError(
              "{func}() couldn't convert argument "
              "{argname}={arg!r} to a pandas Timestamp.\n"
              "Original error was: {t}: {e}".format(
                  func=_qualified_name(func),
                  argname=argname,
                  arg=arg,
                  t=_qualified_name(type(e)),
                  e=e,
              ),
          )
docs: Argument preprocessor that converts the input into a pandas Timestamp
      object.
  
      Examples
      --------
      >>> from zipline.utils.preprocess import preprocess
      >>> @preprocess(ts=ensure_timestamp)
      ... def foo(ts):
      ...     return ts
      >>> foo('2014-01-01')
      Timestamp('2014-01-01 00:00:00')