阻止BufferedReader關閉文件的文件列表

Question

我有一個擴展了BufferedReader的類和一個文件流列表 b.close（）除了最後一個流之外都被調用，我想保持流打開 我該怎麼做？

感謝

 

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

即使在實施BufferedIOBase類包裝的IOBase對象，它們的接口是一個流（一切從IOBase繼承），所以IOBase對象的普通行爲是封閉自己當他們超出範圍。 BufferedIOBase只是將close()調用委託給基礎流。

您不應將BufferedReader視爲流包裝（儘管它是如何實現的），而是作爲對現有流的類型轉換。兩條河流的狀態完全結合在一起。但是，您可以使用detach()取消綁定包裝流，但這會使BufferedIOBase對象無用。

此外，當模式爲rb時，io.open已返回BufferedReader，所以您是雙緩衝。您應該改用io.FileIO。

您有幾種選擇：

1. 創建一個新的物流和新底層的文件描述符，並通過周圍的文件名，而不是流。這是您最簡單和最安全的選擇。

2. 根據需要創建原始文件描述符並根據它們創建流。這需要一些 注意多個流不同時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 
   

3. detach()底層流的BufferedIOBase對象之前關閉其流。 （記住，倒轉流！）

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

   你甚至可以在你的析構函數實現這一點：

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

   或者只是禁用close()代表團完全，如果你認爲語義是錯誤的：

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

我不知道你在做什麼（可能你需要一個不同的des ign），但這是我將如何實現我看到的代碼：

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