實現
定義抽象介面，維護乙個實現者（需要為幫助獲取內容的實現類定義介面）的物件引用
為獲取內容的實現類定義介面：python使用元類和抽象基類（abc）定義等價的介面
實現實現者介面並定義其具體實現
主函式呼叫：
**實現
import abc
import urllib.parse
import urllib.request
class resourcecontent:
"""define the abstraction's inte***ce.
maintain a reference to an object which represents the implementor.
"""def __init__(self, imp):
self._imp = imp
def show_content(self, path):
self._imp.fetch(path)
class resourcecontentfetcher(metaclass=abc.abcmeta):
"""define the inte***ce (implementor) for implementation classes that help fetch content.
"""@abc.abstractmethod
def fetch(path):
pass
class urlfetcher(resourcecontentfetcher):
"""implement the implementor inte***ce and define its concrete
implementation.
"""def fetch(self, path):
# path is an url
req = urllib.request.request(path)
with urllib.request.urlopen(req) as response:
if response.code == 200:
the_page = response.read()
print(the_page)
class localfilefetcher(resourcecontentfetcher):
"""implement the implementor inte***ce and define its concrete
implementation.
"""def fetch(self, path):
# path is the filepath to a text file
with open(path) as f:
print(f.read())
def main():
url_fetcher = urlfetcher()
iface = resourcecontent(url_fetcher)
iface.show_content('')
print('***************====')
localfs_fetcher = localfilefetcher()
iface = resourcecontent(localfs_fetcher)
iface.show_content('file.txt')
if __name__ == "__main__":
main()
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