**實現
import copy
class website:
def __init__(self, name, domain, description, author, **kwargs):
'''examples of optional attributes (kwargs):
category, creation_date, technologies, keywords.
'''
self.name = name
self.domain = domain
self.description = description
self.author = author
for key in kwargs:
setattr(self, key, kwargs[key])
def __str__(self):
summary = [f'website ""\n',]
infos = vars(self).items()
ordered_infos = sorted(infos)
for attr, val in ordered_infos:
if attr == 'name':
continue
return ''.join(summary)
class prototype:
def __init__(self):
self.objects = dict()
def register(self, identifier, obj):
self.objects[identifier] = obj
def unregister(self, identifier):
del self.objects[identifier]
def clone(self, identifier, **attrs):
found = self.objects.get(identifier)
if not found:
raise valueerror(f'incorrect object identifier: ')
obj = copy.deepcopy(found)
for key in attrs:
setattr(obj, key, attrs[key])
return obj
def main():
keywords = ('python', 'data', 'apis', 'automation')
site1 = website('contentgardening',
domain='contentgardening.com',
author='kamon ayeva',
category='blog',
keywords=keywords)
prototype = prototype()
identifier = 'ka-cg-1'
prototype.register(identifier, site1)
site2 = prototype.clone(identifier,
name='contentgardeningplayground',
domain='play.contentgardening.com',
description='experimentation for techniques featured on the blog',
category='membership site',
creation_date='2018-08-01')
for site in (site1, site2):
print(site)
print(f'id site1 : != id site2 : ')
if __name__ == '__main__':
main()
定義website類，並新增前文所示的初始化方法（__init__()）和字串展示方法（__str__()）
定義prototype類
新增main函式
實現
首先為單例模式實現乙個元類，其中元類的__call()__方法確保只能建立乙個類例項
繼承元類
**實現
import urllib.parse
import urllib.request
class singletontype(type):
_instances = {}
def __call__(cls, *args, **kwargs):
if cls not in cls._instances:
cls._instances[cls] = super(singletontype, cls).__call__(*args, **kwargs)
return cls._instances[cls]
class urlfetcher(metaclass=singletontype):
def __init__(self):
self.urls =
def fetch(self, url):
req = urllib.request.request(url)
with urllib.request.urlopen(req) as response:
if response.code == 200:
the_page = response.read()
print(the_page)
urls = self.urls
self.urls = urls
def dump_url_registry(self):
return ', '.join(self.urls)
def main():
my_urls = ['',
'',
'','',
]print(urlfetcher() is urlfetcher())
fetcher = urlfetcher()
for url in my_urls:
try:
fetcher.fetch(url)
except exception as e:
print(e)
print('-------')
done_urls = fetcher.dump_url_registry()
print(f'done urls: ')
if __name__ == '__main__':
main()
單例模式,原型模式,享元模式
這三個模式為什麼放一起呢。都是減少建構函式多次被構造為目的產生的模式。也就是說 a a new a a b new a 這樣就兩次構造了這個物件 單例模式 在它的核心結構中只包含乙個被稱為單例的特殊類。通過單例模式可以保證系統中乙個類只有乙個例項。即乙個類只有乙個物件例項 有乙個廚師 class c...
理解設計模式之單例模式和原型模式
單例模式 就是乙個能保證在整個程序中只有乙個例項的類 一.想實現單例模式首先就不能把建構函式公開 私有化建構函式 1.私有化建構函式 private singleton 二.那如何例項化呢？提供乙個公開的靜態方法。2.公開的靜態方法提供例項 public static singleton creat...
單例和原型模式 建立型
確保乙個特殊類的例項是獨一無二的 它是這個類的唯一例項 並且這個例項易於被訪問。解決方案 1 全域性變數 乙個全域性變數使得乙個物件可以被訪問，但它不能防止你例項化多個物件。因為你的任何 都能修改全域性變數，這將不可避免的引起更多除錯的意外。換句話說，全域性變數的狀態總是會出現一些問題的。2 類建構...