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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sg_input(shape=None, dtype=sg_floatx, name=None):
 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`. """

    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)