code: def plot(self, qubit_subset=None):
          
          import matplotlib.pyplot as plt
          prob_dict = self.get_outcome_probs()
          if qubit_subset:
              sub_dict = {}
              qubit_num = len(self)
              for i in qubit_subset:
                  if i > (2**qubit_num - 1):
                      raise IndexError("Index {} too large for {} qubits.".format(i, qubit_num))
                  else:
                      sub_dict[get_bitstring_from_index(i, qubit_num)] = prob_dict[get_bitstring_from_index(i, qubit_num)]
              prob_dict = sub_dict
          plt.bar(range(len(prob_dict)), prob_dict.values(), align='center', color='#6CAFB7')
          plt.xticks(range(len(prob_dict)), prob_dict.keys())
          plt.show()
docs: Plots a bar chart with bitstring on the x axis and probability on the y axis.
  
          :param list qubit_subset: Optional parameter used for plotting a subset of the Hilbert space.