Fetch logs from all streams under the given CloudWatch Log Group and yields in the output. Optionally, caller
        can filter the logs using a pattern or a start/end time.

        Parameters
        ----------
        log_group_name : string
            Name of CloudWatch Logs Group to query.

        start : datetime.datetime
            Optional start time for logs.

        end : datetime.datetime
            Optional end time for logs.

        filter_pattern : str
            Expression to filter the logs by. This is passed directly to CloudWatch, so any expression supported by
            CloudWatch Logs API is supported here.

        Yields
        ------

        samcli.lib.logs.event.LogEvent
            Object containing the information from each log event returned by CloudWatch Logs

def fetch(self, log_group_name, start=None, end=None, filter_pattern=None):
        """
        Fetch logs from all streams under the given CloudWatch Log Group and yields in the output. Optionally, caller
        can filter the logs using a pattern or a start/end time.

        Parameters
        ----------
        log_group_name : string
            Name of CloudWatch Logs Group to query.

        start : datetime.datetime
            Optional start time for logs.

        end : datetime.datetime
            Optional end time for logs.

        filter_pattern : str
            Expression to filter the logs by. This is passed directly to CloudWatch, so any expression supported by
            CloudWatch Logs API is supported here.

        Yields
        ------

        samcli.lib.logs.event.LogEvent
            Object containing the information from each log event returned by CloudWatch Logs
        """

        kwargs = {
            "logGroupName": log_group_name,
            "interleaved": True
        }

        if start:
            kwargs["startTime"] = to_timestamp(start)

        if end:
            kwargs["endTime"] = to_timestamp(end)

        if filter_pattern:
            kwargs["filterPattern"] = filter_pattern

        while True:
            LOG.debug("Fetching logs from CloudWatch with parameters %s", kwargs)
            result = self.cw_client.filter_log_events(**kwargs)

            # Several events will be returned. Yield one at a time
            for event in result.get('events', []):
                yield LogEvent(log_group_name, event)

            # Keep iterating until there are no more logs left to query.
            next_token = result.get("nextToken", None)
            kwargs["nextToken"] = next_token
            if not next_token:
                break