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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 first_order_gradient(arr, axis=0):
  '''
  Returns the gradient of arr along a particular axis using
  the first order forward-difference.
  Additionally, the result is padded with 0 so that the
  returned array is the same shape as in input array.
  '''
  grad_arr = difference(arr, n=1, axis=axis)
  return np.insert(grad_arr, grad_arr.shape[axis], 0, axis=axis)