Python os.SEEK_SETs 代码实例

Python os.SEEK_SETs 代码实例

实例 1

def fill(self):
        """
        Write the current file full and sync it to disk.  The goal here is
        a contiguous area on disk for this file.
        """
        sys.stderr.write("[commitlog] filling commit log {0:010}n".format(
            self.index
        ))
        # Preferred version would use syscall(2) to call fallocate(2) or
        # directly call posix_fallocate(3).
        #libc = ctypes.CDLL("libc.so.6")
        #libc.syscall(285, self,fd, self.WRITE, 0, self.filesize)
        #libc.posix_fallocate(self.fd, 0, self.filesize)
        # But for now, I'll settle for writing a file full manually and
        # hoping it's contiguous on disk.
        empty = message.Write("" * message.Write.LENGTH)
        while not self.full():
            self.write(empty, False)
        os.fsync(self.fd)
        self.len = 0
        os.lseek(self.fd, 0, os.SEEK_SET)
     

实例 2

def seek(self, pos, whence=os.SEEK_SET):
        """Seek to a position in the file.
        """
        if self.closed:
            raise ValueError("I/O operation on closed file")
        if whence == os.SEEK_SET:
            self.position = min(max(pos, 0), self.size)
        elif whence == os.SEEK_CUR:
            if pos < 0:
                self.position = max(self.position + pos, 0)
            else:
                self.position = min(self.position + pos, self.size)
        elif whence == os.SEEK_END:
            self.position = max(min(self.size + pos, self.size), 0)
        else:
            raise ValueError("Invalid argument")
        self.buffer = ""
        self.fileobj.seek(self.position)
     

实例 3

def _GetRangeData(self, ranges):
    """Generator that produces all the image data in 'ranges'.  The
    number of individual pieces returned is arbitrary (and in
    particular is not necessarily equal to the number of ranges in
    'ranges'.
    This generator is stateful -- it depends on the open file object
    contained in this SparseImage, so you should not try to run two
    instances of this generator on the same object simultaneously."""
    f = self.simg_f
    for s, e in ranges:
      to_read = e-s
      idx = bisect.bisect_right(self.offset_index, s) - 1
      chunk_start, chunk_len, filepos, fill_data = self.offset_map[idx]
      # for the first chunk we may be starting partway through it.
      remain = chunk_len - (s - chunk_start)
      this_read = min(remain, to_read)
      if filepos is not None:
        p = filepos + ((s - chunk_start) * self.blocksize)
        f.seek(p, os.SEEK_SET)
        yield f.read(this_read * self.blocksize)
      else:
        yield fill_data * (this_read * (self.blocksize >> 2))
      to_read -= this_read
      while to_read > 0:
        # continue with following chunks if this range spans multiple chunks.
        idx += 1
        chunk_start, chunk_len, filepos, fill_data = self.offset_map[idx]
        this_read = min(chunk_len, to_read)
        if filepos is not None:
          f.seek(filepos, os.SEEK_SET)
          yield f.read(this_read * self.blocksize)
        else:
          yield fill_data * (this_read * (self.blocksize >> 2))
        to_read -= this_read
   

实例 4

def to_python(self, data):
        d = D({})
        d['filename'] = os.path.basename(data.filename)
        d['file'] = data.file
        data.file.seek(0, os.SEEK_END)
        d['size'] = data.file.tell()
        data.file.seek(0, os.SEEK_SET)
        return d