Question

我有一个扩展BufferedReader的类和一个文件流列表 b.close（）被调用除了最后一个流之外的所有流，我想保持流打开我该怎么做？

感谢


class TestReader(BufferedReader):
    pass

def test(streams):
    for stream in streams:
        b=TestReader(stream)
        do_something(b)
    #all the streams except streams[-1] are closed, how do I prevent this?

streams=[open('test1.txt','rb'),open('test2.txt','rb')]
test(streams)
streams.do_something_else()

Answer 1

即使在实现BufferedIOBase类中包装了一个IOBase对象，它们的接口也是一个流（所有继承自IOBase），所以普通行为IOBase对象的一个是当它们超出范围时关闭它们自己。 BufferedIOBase只是将close()调用委托给基础流。

您不应将BufferedReader视为流包装器（尽管它是如何实现的），而是作为现有流的类型转换。状态两个流完全绑定在一起。但是，您可以使用detach()取消绑定包装的流，但这会使BufferedIOBase对象无效。

此外，当模式为io.open时，BufferedReader已经返回rb，因此您将进行双缓冲。您应该使用io.FileIO代替。

您有几个选择：

创建新流和新的基础文件描述符，并传递文件名而不是流。这是您最简单，最安全的选择。

根据需要创建原始文件描述符并从中创建流。这需要一些注意多个流不同时使用相同的文件描述符。例如：

fd = os.open('test.txt', os.O_RDONLY)
file1 = FileIO(fd, 'r', closefd=False)
file2 = FileIO(fd, 'r', closefd=False)

file1.read(100)
assert file1.tell() == 100
file2.read(100)
assert file1.tell() == 200

detach() BufferedIOBase对象关闭其流之前的基础流。（记得回流一下！）

def test(streams):
    for stream in streams:
        b=TestReader(stream)
        do_something(b)
        wrappedstream = b.detach()
        assert wrappedstream is stream

您甚至可以在析构函数中实现它：

class TestReader(BufferedReader):
    def __del__(self):
        self.detach()
        # self.raw will not be closed,
        # rather left in the state it was in at detachment

如果您认为语义错误，则完全禁用close()委派：

class TestReader(BufferedReader):
    def close(self):
        self.closed = True

我不了解你在做什么（可能你需要一个不同的设计），但这就是我实现我看到的代码的方式：

from io import FileIO, BufferedReader
import io
import os

class TestReader(BufferedReader):
    pass

def test(streams):
    for stream in streams:
        b = TestReader(stream)

def test_reset(streams):
    """Will try to leave stream state unchanged"""
    for stream in streams:
        pos = stream.tell()
        b = TestReader(stream)
        do_something(b)
        b.detach()
        stream.seek(pos)



filenames = ['test1.txt', 'test2.txt']

# option 1: just make new streams

streams = [FileIO(name, 'r') for name in filenames]
test(streams)
streams = [io.open(name, 'rb') for name in filenames]
#etc


# option 2: use file descriptors
fds = [os.open(name, os.O_RDONLY) for name in filenames]
#closefd = False means "do not close fd on __del__ or __exit__"
#this is only an option when you pass a fd instead of a file name
streams = [FileIO(fd, 'r', closefd=False) for fd in fds]
test(streams)
streams = []
for fd in fds:
    os.lseek(fd, 0, os.SEEK_SET)
    streams.append(io.open(fd, 'rb', closefd=False))
    # you can also .seek(0) on the BufferedReader objects
    # instead of os.lseek on the fds


# option 3: detach

streams = [FileIO(name, 'r') for name in filenames]
test_reset(streams)
# streams[*] should still be in the same state as when you passed it in

防止BufferedReader关闭文件列表中的文件

1 个答案: