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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 async def call(self, method, **params):
 """ Call an Slack Web API method :param method: Slack Web API method to call :param params: {str: object} parameters to method :return: dict() """

        url = self.SLACK_RPC_PREFIX + method
        data = FormData()
        data.add_fields(MultiDict(token=self.bot_token, charset='utf-8', **params))
        response_body = await self.request(
            method='POST',
            url=url,
            data=data
        )
        if 'warning' in response_body:
            logger.warning(f'Warnings received from API call {method}: {response_body["warning"]}')
        if 'ok' not in response_body:
            logger.error(f'No ok marker in slack API call {method} {params} => {response_body}')
            raise SlackCallException('There is no ok marker, ... strange', method=method)
        if not response_body['ok']:
            logger.error(f'Slack API call failed {method} {params} => {response_body}')
            raise SlackCallException(f'No OK response returned', method=method)
        return response_body