buffered_part_reader.py 文件源码

def __init__(self, file_object, start, size):
        """
        Build an object that will act like a BufferedReader object,
        but constrained to a predetermined part of the file_object.

        :param file_object: A file opened for reading in binary mode.
        :param start: Start of the part within the file_object
        :param size: Ideal size of the part.  This will be set
                     to the number of bytes remaining in the
                     file if there aren't enough bytes remaining.
        """
        self.file = file_object
        self.bytes_read = 0
        self.start = start

        # Seek to the end of the file to see how many bytes remain
        # from the start of the part.
        self.file.seek(0, io.SEEK_END)
        self.size = min(self.file.tell() - self.start, size)

        # Reset the pointer to the start of the part.
        self.file.seek(start, io.SEEK_SET)