def arithmetic_mean(X):
  """Computes the arithmetic mean of the sequence `X`.

  Let:

    * `n = len(X)`.
    * `u` denote the arithmetic mean of `X`.

  .. math::

    u = \frac{\sum_{i = 0}^{n - 1} X_i}{n}
  """
  return sum(X) / len(X)