using espression on a list with Python DatastreamDSWS

Hi, i'm beginning using https://github.com/DatastreamDSWS/Datastream to get the market capitalisation for a list, namely the constituents of an index e.g. with this request ds.get_data(tickers="LS1ESU1E|L",fields =["MV"], kind=0) i was wondering if it's possible to apply an expression, namely the sum of all MV for the constituents to get the value but i can't combine expression with list and i did not find a similar example around, many thanks in advance Paolo