code: def proportion_difference(proportion_1, proportion_2, n_1, n_2=None):
      """
      Computes the test statistic and p-value for a difference of
      proportions test.
  
      Parameters
      -----------
      proportion_1 : float
          The first proportion
      proportion_2 : float
          The second proportion
      n_1 : int
          The sample size of the first test sample
      n_2 : int or None (default=None)
          The sample size of the second test sample.
          If `None`, `n_1`=`n_2`.
  
      Returns
      -----------
  
      z, p : float or None, float
          Returns the z-score and the p-value
  
  
      Examples
      -----------
      For usage examples, please see
      https://rasbt.github.io/mlxtend/user_guide/evaluate/proportion_difference/
  
      """
      if n_2 is None:
          n_2 = n_1
  
      var_1 = proportion_1 * (1.0 - proportion_1) / n_1
      var_2 = proportion_2 * (1.0 - proportion_2) / n_2
  
      z = (proportion_1 - proportion_2) / np.sqrt(var_1 + var_2)
      p = scipy.stats.norm.cdf(z)
  
      return z, p
  
label_desc: Use image node_id 1 for calling a global function with example usage: proportion_difference(proportion_1, proportion_2, n_1, n_2) and returns: z,  p