code: def replace(self, str1, str2):
          
          if str2 != self._replacements.get(str1, None):
              self._replacements[str1] = str2
              self.changed(code_changed=True)
docs: Set verbatim code replacement
          
          It is strongly recommended to use function['$foo'] = 'bar' where
          possible because template variables are less likely to changed
          than the code itself in future versions of vispy.
          
          Parameters
          ----------
          str1 : str
              String to replace
          str2 : str
              String to replace str1 with