DynamoDB update_item() is convoluted, requiring placeholders and name maps to avoid 572 reserved keywords; this seems a pretty concise approach to mapping a dict to names it will accept.

dynamodb_update_item.py

def asset_update(asset_id, state, extra={}):
    asset = extra.copy()
    asset.update({'dt': datetime.now().isoformat(),
                  'state': state})

    # We need update_item placeholder and values like:
    #   UpdateExpression='SET dt = :dt, #state = :state'   # 'state' is a reserved word
    #   ExpressionAttributeNames={'#state': 'state'}       # proxy for reserved word 'state'
    #   ExpressionAttributeValues={':dt': datetime.now().isoformat(), ':state': 'uploaded'}
    # We can't use "reserved words" like 'state' use EAN for *all* names,
    # since we don't know _a priori_ the names that will be submitted.

    ue = 'SET ' + ', '.join('#{} = :{}'.format(k, k) for k in asset.keys())
    ean = {'#' + k: k for k in asset}
    eav = {':' + k: v for k, v in asset.items()}
    log.debug('asset_update ue={}'.format(ue))
    log.debug('asset_update ean={}'.format(json.dumps(ean)))
    log.debug('asset_update eav={}'.format(json.dumps(eav)))
    try:
        assetsdb.update_item(Key={'id': asset_id},
                             UpdateExpression=ue,
                             ExpressionAttributeNames=ean,
                             ExpressionAttributeValues=eav)
    except (ClientError, BotoCoreError) as e:
        raise Exception('[ServerError] update_item id={}: {}'.format(asset_id, e))