外观模式(learning_python_design_patterns)

Facades外观模式经常在python的源码中出现

給复杂的系統提供簡單的接口

import urllib
import requests
class WeatherProvider(object):
    def __init__(self):
        self.api_url = 'https://samples.openweathermap.org/data/2.5/weather?q={},{}'

    def get_weather_data(self, city, country):
        city = urllib.parse.quote(city)
        print(city)
        url = self.api_url.format(city, country)
        print(url)
        return requests.get(url).text


from datetime import datetime
import json

class Parser(object):

    def parse_weather_data(self, weather_data):
        parsed = json.loads(weather_data)
        start_date = None
        result = []
        for data in parsed['list']:
            date = datetime.strptime(data['dt_txt'], '%Y-%m-%d %H:%M:%S')
            start_date = start_date or date
            if start_date.day != date.day:
                return result

            result.append(data['main']['temp'])



from datetime import timedelta
import pickle

class Cache(object):
    def __init__(self, filename):
        self.filename = filename

    def save(self, obj):
        with open(self.filename, 'w') as file:
            dct = {
            'obj': obj,
            'expired': datetime.utcnow() + timedelta(hours=3)
            }
            pickle.dump(dct, file)

    def load(self):
        try:
            with open(self.filename) as file:
                result = pickle.load(file)
                if result['expired'] > datetime.utcnow():
                    return result['obj']
        except IOError:
            pass


class Converter(object):
     def from_kelvin_to_celcius(self, kelvin):
        return kelvin - 273.15


class Weather(object):
     def __init__(self, data):
         result = 0
         for r in data:
             result += r
         self.temperature = result / len(data)



class Facade(object):
     def get_forecast(self, city, country):
         cache = Cache('myfile')
         cache_result = cache.load()
         if cache_result:
             return cache_result

         else:
             weather_provider = WeatherProvider()
             weather_data = weather_provider.get_weather_data(city, country)
             print(weather_data)
             parser = Parser()
             parsed_data = parser.parse_weather_data(weather_data)
             weather = Weather(parsed_data)
             converter = Converter()
             temperature_celcius = converter.from_kelvin_to_celcius(weather.
                                                                    temperature)
             cache.save(temperature_celcius)
             return temperature_celcius


if __name__ == '__main__':
    facade = Facade()
    print(facade.get_forecast('London', 'UK'))