Return the next line in the source.

        :param require_prefix:  if False, the whole line will be returned.
            otherwise, return the line with prefix stripped or None if the prefix
            is not matched.

def next_line(self, require_prefix=True):
        """Return the next line in the source.

        :param require_prefix:  if False, the whole line will be returned.
            otherwise, return the line with prefix stripped or None if the prefix
            is not matched.
        """
        if require_prefix:
            m = self.expect_re(r'(?m)[^\n]*?$\n?')
        else:
            m = self._expect_re(r'(?m)[^\n]*$\n?', self.pos)
        self.match = m
        if m:
            return m.group()