python内置模块之上下文管理contextlib

with open('/path/filename', 'r') as f:
    f.read()

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()

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()

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

from contextlib import closing
from urllib.request import urlopen
 
with closing(urlopen('https://www.python.org')) as page:
    for line in page:
        print(line)

@contextmanager
def closing(thing):
    try:
        yield thing
    finally:
        thing.close()