python中文件的问题

oneouts

使用
    rs=open(‘filename’，‘w')
    打开一个文件，
    然后写入，但是这个写入值大小不定
    rs.close()
    sleep（5)
..#在对这个文件进行其他操作

问题就在这里写入的东西大小不定，rs.close()后需要时间将文件写入filename中，所以才是使用sleep，如何判断文件是否
完全写入，减少sleep的时间？？

crifan

用rs.close()之前，先去使用rs.flush()，即可将数据（同步）写回。
然后再close，不用sleep，就可以保证数据是安全写入的了。
刚看了官网的解释：

file.flush()
Flush the internal buffer, like stdio‘s fflush(). This may be a no-op on some file-like objects.

Note
flush() does not necessarily write the file’s data to disk. Use flush() followed by os.fsync() to ensure this behavior.

所以，更按安全的做法是，

1. rs.flush();
   
2. os.fsync(rs);
   
3. rs.close();

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这样，就完全确保数据已经真在写入了。
就不用再sleep了。

linux_c_py_php

楼上正解.

1. 
   
2. NAME
   
3.        fsync, fdatasync - synchronize a file’s in-core state with storage device
   
4. 
   
5. SYNOPSIS
   
6.        #include <unistd.h>
   
7. 
   
8.        int fsync(int fd);
   
9. 
   
10.        int fdatasync(int fd);
    
11. 
    
12.    Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
    
13. 
    
14.        fsync(): _BSD_SOURCE || _XOPEN_SOURCE
    
15.                 || /* since glibc 2.8: */ _POSIX_C_SOURCE >= 200112L
    
16.        fdatasync(): _POSIX_C_SOURCE >= 199309L || _XOPEN_SOURCE >= 500
    
17. 
    
18. DESCRIPTION
    
19.        fsync()  transfers  ("flushes") all modified in-core data of (i.e., modified buffer cache pages for) the file referred to by the file descriptor
    
20.        fd to the disk device (or other permanent storage device) so that all changed information can be retrieved even after the system crashed or  was
    
21.        rebooted.   This  includes  writing through or flushing a disk cache if present.  The call blocks until the device reports that the transfer has
    
22.        completed.  It also flushes metadata information associated with the file (see stat(2)).
    
23. 
    
24.        Calling fsync() does not necessarily ensure that the entry in the directory containing the file has also reached disk.   For  that  an  explicit
    
25.        fsync() on a file descriptor for the directory is also needed.
    
26. 
    
27.        fdatasync()  is  similar  to  fsync(),  but  does not flush modified metadata unless that metadata is needed in order to allow a subsequent data
    
28.        retrieval to be correctly handled.  For example, changes to st_atime or st_mtime (respectively, time of last access and time of  last  modifica-
    
29.        tion;  see  stat(2))  do  not  require flushing because they are not necessary for a subsequent data read to be handled correctly.  On the other
    
30.        hand, a change to the file size (st_size, as made by say ftruncate(2)), would require a metadata flush.
    
31. 
    
32.        The aim of fdatasync() is to reduce disk activity for applications that do not require all metadata to be synchronized with the disk.

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oneouts

十分感谢两位