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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 L1(layer="input", constant=0, batch=None):
 """L1 norm of layer. Generally used as penalty."""

  if batch is None:
    return lambda T: tf.reduce_sum(tf.abs(T(layer) - constant))
  else:
    return lambda T: tf.reduce_sum(tf.abs(T(layer)[batch] - constant))