python 装饰器：contextlib
上下文环境：
开始信息
|
中间输出信息
|
结束信息
上下文环境1：
#!/usr/bin/python
# -*- coding: utf-8 -*-
class Query(object):
def __init__(self, name):
self.name = name
def __enter__(self):
print('Begin')
return self
def __exit__(self, exc_type, exc_value, traceback):
if exc_type:
print('Error')
else:
print('End')
def query(self):
print('Query info about %s...' % self.name)
with Query('Bob') as q:
q.query()
Query('Bob').query()
运行结果：
Begin Query info about Bob... End Query info about Bob...
上下文环境2：@contextmanager
from contextlib import contextmanager
class Query(object):
def __init__(self, name):
self.name = name
def query(self):
print('Query info about %s...' % self.name)
@contextmanager
def create_query(name):
print('Begin')
q = Query(name)
yield q
print('End')
with create_query('Bob') as q:
q.query()
运行结果：
Begin Query info about Bob... End
上下文环境3：@contextmanager 再次简化
from contextlib import contextmanager
@contextmanager
def tag(name):
print("<%s>" % name)
yield
print("</%s>" % name)
with tag("h2"):
print("hello")
print("world")
上述代码执行结果为：
<h2> hello world </h2>
没有上下文环境：@closing 通过closing()来把该对象变为上下文对象，例如，用with语句使用urlopen()：
from contextlib import closing
from urllib.request import urlopen
with closing(urlopen('https://www.baidu.com')) as page:
for line in page:
print(line)
上述代码执行结果为：
b'<html>\r\n'
b'<head>\r\n'
b'\t<script>\r\n'
b'\t\tlocation.replace(location.href.replace("https://","http://"));\r\n'
b'\t</script>\r\n'
b'</head>\r\n'
b'<body>\r\n'
b'\t<noscript><meta http-equiv="refresh" content="0;url=http://www.baidu.com/"></noscript>\r\n'
b'</body>\r\n'
b'</html>'
不懂怎么验证的closing
from contextlib import contextmanager @contextmanager def closing(thing): try: yield thing finally: thing.close()
上述代码执行结果为：