def parse_cron(self, value):
    'Check for valid cron string.'
    fields = value.split()
    if ((len(fields) == 5) and all([self.cron_rx.match(i) for i in fields])):
        return True
    return False
Check for valid cron string.
def parse_cron(self, value):
    
    fields = value.split()
    if ((len(fields) == 5) and all([self.cron_rx.match(i) for i in fields])):
        return True
    return False