Return a SourceLine of the current line.

def get_current_line(self):
        """Return a SourceLine of the current line."""
        if not self.has_space():
            return None

        pos = self.pos - self.col
        string = self.string
        end = self.length

        output = []
        while pos < len(string) and string[pos] != '\n':
            output.append(string[pos])
            pos += 1
            if pos == end:
                break
        else:
            output.append(string[pos])

        if not output:
            return None

        return SourceLine(''.join(output), self.row)