def readline(self, limit=-1):
        """Read and return a line from the stream.

        If limit is specified, at most limit bytes will be read.
        """

        if not self._universal and limit < 0:
            # Shortcut common case - newline found in buffer.
            i = self._readbuffer.find(b'\n', self._offset) + 1
            if i > 0:
                line = self._readbuffer[self._offset: i]
                self._offset = i
                return line

        if not self._universal:
            return io.BufferedIOBase.readline(self, limit)

        line = b''
        while limit < 0 or len(line) < limit:
            readahead = self.peek(2)
            if readahead == b'':
                return line

            #
            # Search for universal newlines or line chunks.
            #
            # The pattern returns either a line chunk or a newline, but not
            # both. Combined with peek(2), we are assured that the sequence
            # '\r\n' is always retrieved completely and never split into
            # separate newlines - '\r', '\n' due to coincidental readaheads.
            #
            match = self.PATTERN.search(readahead)
            newline = match.group('newline')
            if newline is not None:
                if self.newlines is None:
                    self.newlines = []
                if newline not in self.newlines:
                    self.newlines.append(newline)
                self._offset += len(newline)
                return line + b'\n'

            chunk = match.group('chunk')
            if limit >= 0:
                chunk = chunk[: limit - len(line)]

            self._offset += len(chunk)
            line += chunk

        return line
Read and return a line from the stream.

        If limit is specified, at most limit bytes will be read.