Python在with关键字范围内延长变量的生存期

假设我的代码打开一个带有

和

关键字的文件，并且我希望它在特定条件下关闭后保持打开状态

假设最简单的函数：

def do_sth():
  with open('/tmp/foobar') as f:
    # do anything to stop f from closing

有没有办法绕过python解释器来调用

f.\uuuu exit\uuu（）

？ 您可以假设，这应该适用于任何实现

\uuuuuuuuuuuuuuuuuuuu

和

\uuuuuuuuuuuuuu

的类

到目前为止，我尝试用另一个可关闭对象替换f，如下所示：

d = open('/tmp/bsdf')
with open('/tmp/asdf') as f:
    d,f = f,d
print "f {}, d {}".format(f.closed, d.closed)

一个潜在的用例是创建一个包装器，这样您就可以：

with filehandle('foobar') as f:
  # do something

# don't close if filehandle returns sys.stdout.

阅读之后，我得出结论，这不应该是语义学的一部分

我找到的唯一选择是编写自己的上下文管理器，它执行有条件的发布

from contextlib import contextmanager
import sys

@contextmanager
def custom_open(filename, mode='r'):
    if filename is 'stdout':
        yield sys.stdout
    else:
        try:
            f = open(filename, mode)
        except IOError, err:
            yield None
        else:
            try:
                yield f
            finally:
                f.close()


with custom_open('stdout') as f:
    f.write('hello world\n')
print "f {}".format(f.closed)

with custom_open('/tmp/foobar', 'w+') as f:
    f.write('hello world\n')
print "f {}".format(f.closed)