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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def read(self, size=-1):
 """Read up to size bytes from the object and return them."""

        if size == 0:
            return b''
        elif size < 0:
            from_buf = self._read_from_buffer()
            self._current_pos = self._content_length
            return from_buf + self._raw_reader.read()

        #
        # Return unused data first
        #
        if len(self._buffer) >= size:
            return self._read_from_buffer(size)

        #
        # If the stream is finished, return what we have.
        #
        if self._eof:
            return self._read_from_buffer()

        #
        # Fill our buffer to the required size.
        #
        # logger.debug('filling %r byte-long buffer up to %r bytes', len(self._buffer), size)
        self._fill_buffer(size)
        return self._read_from_buffer(size)