解释器模式（Interpreter Pattern）提供了评估语言的语法或表达式的方式，它属于行为型模式。这种模式实现了一个表达式接口，该接口解释一个特定的上下文。这种模式被用在 SQL 解析、符号处理引擎等。
对每个应用来说，至少有以下两种不同的用户分类。
? 基本用户：这类用户只希望能够凭直觉使用应用。他们不喜欢花太多时间配置或学习应
用的内部。对他们来说，基本的用法就足够了。
? 高级用户：这些用户，实际上通常是少数，不介意花费额外的时间学习如何使用应用的
高级特性。如果知道学会之后能得到以下好处，他们甚至会去学习一种配置（或脚本）
语言。
? 能够更好地控制一个应用
? 以更好的方式表达想法
? 提高生产力
解释器（Interpreter）模式仅能引起应用的高级用户的兴趣。这是因为解释器模式背后的主
要思想是让非初级用户和领域专家使用一门简单的语言来表达想法。然而，什么是一种简单的语
言？对于我们的需求来说，一种简单的语言就是没编程语言那么复杂的语言
# coding: utf-8 from pyparsing import Word, OneOrMore, Optional, Group, Suppress, alphanums class Gate: def __init__(self): self.is_open = False def __str__(self): return ‘open‘ if self.is_open else ‘closed‘ def open(self): print(‘opening the gate‘) self.is_open = True def close(self): print(‘closing the gate‘) self.is_open = False class Garage: def __init__(self): self.is_open = False def __str__(self): return ‘open‘ if self.is_open else ‘closed‘ def open(self): print(‘opening the garage‘) self.is_open = True def close(self): print(‘closing the garage‘) self.is_open = False class Aircondition: def __init__(self): self.is_on = False def __str__(self): return ‘on‘ if self.is_on else ‘off‘ def turn_on(self): print(‘turning on the aircondition‘) self.is_on = True def turn_off(self): print(‘turning off the aircondition‘) self.is_on = False class Heating: def __init__(self): self.is_on = False def __str__(self): return ‘on‘ if self.is_on else ‘off‘ def turn_on(self): print(‘turning on the heating‘) self.is_on = True def turn_off(self): print(‘turning off the heating‘) self.is_on = False class Boiler: def __init__(self): self.temperature = 83 # in celsius def __str__(self): return ‘boiler temperature: {}‘.format(self.temperature) def increase_temperature(self, amount): print("increasing the boiler‘s temperature by {} degrees".format(amount)) self.temperature += amount def decrease_temperature(self, amount): print("decreasing the boiler‘s temperature by {} degrees".format(amount)) self.temperature -= amount class Fridge: def __init__(self): self.temperature = 2 # 单位为摄氏度 def __str__(self): return ‘fridge temperature: {}‘.format(self.temperature) def increase_temperature(self, amount): print("increasing the fridge‘s temperature by {} degrees".format(amount)) self.temperature += amount def decrease_temperature(self, amount): print("decreasing the fridge‘s temperature by {} degrees".format(amount)) self.temperature -= amount def main(): word = Word(alphanums) command = Group(OneOrMore(word)) token = Suppress("->") device = Group(OneOrMore(word)) argument = Group(OneOrMore(word)) event = command + token + device + Optional(token + argument) gate = Gate() garage = Garage() airco = Aircondition() heating = Heating() boiler = Boiler() fridge = Fridge() tests = (‘open -> gate‘, ‘close -> garage‘, ‘turn on -> aircondition‘, ‘turn off -> heating‘, ‘increase -> boiler temperature -> 5 degrees‘, ‘decrease -> fridge temperature -> 2 degrees‘) open_actions = {‘gate‘: gate.open, ‘garage‘: garage.open, ‘aircondition‘: airco.turn_on, ‘heating‘: heating.turn_on, ‘boiler temperature‘: boiler.increase_temperature, ‘fridge temperature‘: fridge.increase_temperature} close_actions = {‘gate‘: gate.close, ‘garage‘: garage.close, ‘aircondition‘: airco.turn_off, ‘heating‘: heating.turn_off, ‘boiler temperature‘: boiler.decrease_temperature, ‘fridge temperature‘: fridge.decrease_temperature} for t in tests: if len(event.parseString(t)) == 2: # 没有参数 cmd, dev = event.parseString(t) cmd_str, dev_str = ‘ ‘.join(cmd), ‘ ‘.join(dev) if ‘open‘ in cmd_str or ‘turn on‘ in cmd_str: open_actions[dev_str]() elif ‘close‘ in cmd_str or ‘turn off‘ in cmd_str: close_actions[dev_str]() elif len(event.parseString(t)) == 3: # 有参数 cmd, dev, arg = event.parseString(t) cmd_str, dev_str, arg_str = ‘ ‘.join(cmd), ‘ ‘.join(dev), ‘ ‘.join(arg) num_arg = 0 try: num_arg = int(arg_str.split()[0]) # 抽取数值部分 except ValueError as err: print("expected number but got: ‘{}‘".format(arg_str[0])) if ‘increase‘ in cmd_str and num_arg > 0: open_actions[dev_str](num_arg) elif ‘decrease‘ in cmd_str and num_arg > 0: close_actions[dev_str](num_arg) if __name__ == ‘__main__‘: main()
