code: def fock_expectation(cov, mu, params, hbar=2.0):
      r"""Calculates the expectation and variance of a Fock state probability.
  
      Args:
          cov (array): :math:`2N\times 2N` covariance matrix
          mu (array): length-:math:`2N` vector of means
          params (Sequence[int]): the Fock state to return the expectation value for
          hbar (float): (default 2) the value of :math:`\hbar` in the commutation
              relation :math:`[\x,\p]=i\hbar`
  
      Returns:
          tuple: the Fock state expectation and variance
      """
      # pylint: disable=unused-argument
      ex = fock_prob(cov, mu, params[0], hbar=hbar)
  
      # var[|n><n|] = E[|n><n|^2] -  E[|n><n|]^2 = E[|n><n|] -  E[|n><n|]^2
      var = ex - ex**2
      return ex, var
  
imports: import math
  import cmath
  import numpy
  from scipy.special import factorial
  import pennylane
  from pennylane.ops import Identity
  from pennylane import Device
  from .._version import __version__
label_desc: Use image node_id 23 for calling a global function with example usage: fock_expectation(cov, mu, params, hbar) and returns: ex,  var