pick list[ : + rest list[:ilist[ + :for in subset(restsize- )result append(pick xreturn result def combo(listsize)if size = or not listreturn [list[: ]elseresult [for in range( (len(listsize )pick list[ : + rest list[ + :for in combo(restsize )result append(pick xreturn result sequence slice keep [:ipart order doesn' matter xyz =yzx iff enough left drop [:ipart all three of these functions work on any sequence object that supports lenslicingand concatenation operations for instancewe can use permute on instances of some of the stack classes defined at the start of this (experiment with this on your own for more insightsthe following session shows our sequence shufflers in action permuting list enables us to find all the ways the items can be arranged for instancefor four-item listthere are possible permutations ( after picking one of the four for the first positionthere are only three left to choose from for the secondand so on order matters[ , , is not the same as [ , , ]so both appear in the resultc:\pp \dstruct\classicspython from permcomb import permute([ ][[ ][ ][ ][ ][ ][ ]permute('abc'['abc''acb''bac''bca''cab''cba'permute('help'['help''hepl''hlep''hlpe''hpel''hple''ehlp''ehpl''elhp''elph''ephl''eplh''lhep''lhpe''lehp''leph''lphe''lpeh''phel''phle''pehl''pelh''plhe''pleh'combo results are related to permutationsbut fixed-length constraint is put on the resultand order doesn' matterabc is the same as acbso only one is added to the result setcombo([ ] [[ ]combo('abc' ['abc'combo('abc' ['ab''ac''bc'combo('abc' [combo(( ) data structures