docs: def set_breakpoint(self, file_name, line_number, condition=None, enabled=True):
          """ Create a breakpoint, register it in the class's lists and returns
          a tuple of (error_message, break_number)
          """
          c_file_name = self.canonic(file_name)
          import linecache
          line = linecache.getline(c_file_name, line_number)
          if not line:
              return "Line %s:%d does not exist." % (c_file_name, line_number), None
          bp = IKBreakpoint(c_file_name, line_number, condition, enabled)
          if self.pending_stop or IKBreakpoint.any_active_breakpoint:
              self.enable_tracing()
          else:
              self.disable_tracing()
          return None, bp.number