pyparsing.py 文件源码

def addCondition(self, *fns, **kwargs):
        """Add a boolean predicate function to expression's list of parse actions. See 
        L{I{setParseAction}<setParseAction>} for function call signatures. Unlike C{setParseAction}, 
        functions passed to C{addCondition} need to return boolean success/fail of the condition.

        Optional keyword arguments:
         - message = define a custom message to be used in the raised exception
         - fatal   = if True, will raise ParseFatalException to stop parsing immediately; otherwise will raise ParseException

        Example::
            integer = Word(nums).setParseAction(lambda toks: int(toks[0]))
            year_int = integer.copy()
            year_int.addCondition(lambda toks: toks[0] >= 2000, message="Only support years 2000 and later")
            date_str = year_int + '/' + integer + '/' + integer

            result = date_str.parseString("1999/12/31")  # -> Exception: Only support years 2000 and later (at char 0), (line:1, col:1)
        """
        msg = kwargs.get("message", "failed user-defined condition")
        exc_type = ParseFatalException if kwargs.get("fatal", False) else ParseException
        for fn in fns:
            def pa(s,l,t):
                if not bool(_trim_arity(fn)(s,l,t)):
                    raise exc_type(s,l,msg)
            self.parseAction.append(pa)
        self.callDuringTry = self.callDuringTry or kwargs.get("callDuringTry", False)
        return self