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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 batch_flatten(x):
 """ Flatten the tensor except the first dimension. """

    shape = x.get_shape().as_list()[1:]
    if None not in shape:
        return tf.reshape(x, [-1, int(np.prod(shape))])
    return tf.reshape(x, tf.stack([tf.shape(x)[0], -1]))