code: def run_bootstrap_post_init(self, config):
          
          cmd = config.get('post_bootstrap') or config.get('post_init')
          if cmd:
              r = self._local_connect_kwargs
  
              if 'host' in r:
                  # '/tmp' => '%2Ftmp' for unix socket path
                  host = quote_plus(r['host']) if r['host'].startswith('/') else r['host']
              else:
                  host = ''
  
                  # https://www.postgresql.org/docs/current/static/libpq-pgpass.html
                  # A host name of localhost matches both TCP (host name localhost) and Unix domain socket
                  # (pghost empty or the default socket directory) connections coming from the local machine.
                  r['host'] = 'localhost'  # set it to localhost to write into pgpass
  
              if 'user' in r:
                  user = r['user'] + '@'
              else:
                  user = ''
                  if 'password' in r:
                      import getpass
                      r.setdefault('user', os.environ.get('PGUSER', getpass.getuser()))
  
              connstring = 'postgres://{0}{1}:{2}/{3}'.format(user, host, r['port'], r['database'])
              env = self.write_pgpass(r) if 'password' in r else None
  
              try:
                  ret = self.cancellable_subprocess_call(shlex.split(cmd) + [connstring], env=env)
              except OSError:
                  logger.error('post_init script %s failed', cmd)
                  return False
              if ret != 0:
                  logger.error('post_init script %s returned non-zero code %d', cmd, ret)
                  return False
          return True
docs: runs a script after initdb or custom bootstrap script is called and waits until completion.