def get_parameter(key):
            """
            function that finds and returns the value for a placeholder.
            """
            if key in param_dict:
                # was a supplied parameter
                param = param_dict.get(key)
            elif module and hasattr(module, key):
                param = getattr(module, key)
                if hasattr(param, "__call__"):
                    # we don't allow module methods
                    raise Exception()
            elif attr_getter:
                # get value from attr_getter function
                try:
                    param = attr_getter(key)
                except:  # noqa e722
                    raise Exception()
            else:
                raise Exception()
            if isinstance(param, Composite):
                if param.text():
                    param = param.copy()
                else:
                    param = ""
            return param

            function that finds and returns the value for a placeholder.
            
py3status/formatter.py