Python编程：contextlib模块实现上下文管理

class Query(object):
    def __init__(self, name):
        self.name = name
    def __enter__(self):
        print("enter")
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
    # 异常类型、异常值、异常追踪信息
        if exc_type:
            print("error")
        else:
            print("end")
    def query(self):
        print("query...")
with Query("Tom") as q:
    q.query()
"""
enter
query...
end
"""

from contextlib import contextmanager
@contextmanager
def tag(name):
    print("<%s>"% name)
    yield
    print("<%s>"% name)
with tag("h1"):
    print("hello world")
"""
<h1>
hello world
<h1>
"""

from contextlib import closing
from urllib.request import urlopen
with closing(urlopen("http://www.baidu.com")) as page:
    print(page.status)
"""
200
"""