docs: def _get_flux_bounds(self, r_id, model, flux_limits, equation):
          """Read reaction's limits to set up strings for limits in the output file.
          """
          if r_id not in flux_limits or flux_limits[r_id][0] is None:
              if equation.direction == Direction.Forward:
                  lower = 0
              else:
                  lower = -model.default_flux_limit
          else:
              lower = flux_limits[r_id][0]
  
          if r_id not in flux_limits or flux_limits[r_id][1] is None:
              if equation.direction == Direction.Reverse:
                  upper = 0
              else:
                  upper = model.default_flux_limit
          else:
              upper = flux_limits[r_id][1]
  
          if lower % 1 == 0:
              lower = int(lower)
          if upper % 1 == 0:
              upper = int(upper)
          return text_type(lower), text_type(upper)