上下文管理contextlib

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)
    try:
        yield q
    finally:
        print('End')

with create_query("zhangsan") as zs:
    zs.query()

输出

Begin
Query info about zhangsan...
End

 

import contextlib

@contextlib.contextmanager
def open_func(file_name):
    # __enter__方法
    print('open file:', file_name, 'in __enter__')
    file_handler = open(file_name, 'r')

    # 【重点】：yield
    yield file_handler

    # __exit__方法
    print('close file:', file_name, 'in __exit__')
    file_handler.close()
    return

with open_func('D:/cloud/cloud-init-19.1.10/tox.ini') as file_in:
    for line in file_in:
        print(line)

 

cosling

返回一个在语句块执行完成时关闭 things 的上下文管理器。这基本上等价于

from contextlib import contextmanager

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

from contextlib import closing
from urllib.request import urlopen

with closing(urlopen('http://www.python.org')) as page:
    for line in page:
        print(line)