code: def sg_input(shape=None, dtype=sg_floatx, name=None):
      r
      if shape is None:
          return tf.placeholder(dtype, shape=None, name=name)
      else:
          if not isinstance(shape, (list, tuple)):
              shape = [shape]
          return tf.placeholder(dtype, shape=[None] + list(shape), name=name)
docs: r"""Creates a placeholder.
  
      Args:
        shape: A tuple/list of integers. If an integers is given, it will turn to a list.
        dtype: A data type. Default is float32.
        name: A name for the placeholder.
  
      Returns:
        A wrapped placeholder `Tensor`.