<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _get_section_start_index(self, section):
        '''Get start of a section's content.

        :param section: string name of section
        :return: integer index of section's beginning
        :raises: NonextantSectionException
        '''

        sec_start_re = r'%s\s*\{' % section

        found = re.search(sec_start_re, self.template_str)
        if found:
            return found.end() - 1

        raise NonextantSectionException(
            'Section %s not found in template' % section
            )