假设我有使用with
关键字打开文件的代码,并且我希望它在某些情况下关闭后保持打开状态。
所以假设最简单的功能:
def do_sth():
with open('/tmp/foobar') as f:
# do anything to stop f from closing
有没有一种方法可以绕过python解释器调用
f.__exit__()
?您可以假定,这应该适用于实现
__enter__
和__exit__
的任何类。到目前为止,我试图用另一个可关闭的对象替换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,以便您可以执行以下操作:
with filehandle('foobar') as f:
# do something
# don't close if filehandle returns sys.stdout.
最佳答案
阅读pep-0343之后,我得出结论,这不应该是语义的一部分。
我发现的唯一选择是编写自己的执行条件释放的上下文管理器。
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)