code: def log_histogram(self, name, value, step=None):
          
          if isinstance(value, six.string_types):
              raise TypeError('"value" should be a number, got {}'
                              .format(type(value)))
  
          self._check_step(step)
          tf_name = self._ensure_tf_name(name)
  
          summary = self._histogram_summary(tf_name, value, step=step)
          self._log_summary(tf_name, summary, value, step=step)
docs: Log a histogram for given name on given step.
  
          Args:
              name (str): name of the variable (it will be converted to a valid
                  tensorflow summary name).
              value (tuple or list): either list of numbers
                  to be summarized as a histogram, or a tuple of bin_edges and
                  bincounts that directly define a histogram.
              step (int): non-negative integer used for visualization