#NEWLINE# def build_mask( self , array ) : #NEWLINE# #INDENT# '\n        Helper for constructing an AssetExists mask from a boolean-coercible\n        array.\n        ' #NEWLINE# ( ndates , nassets ) = array . shape #NEWLINE# return DataFrame ( array , index = self . __calendar [ ( - ndates ) : ] , columns = self . __assets [ : nassets ] , dtype = bool )