def select_var(selfiter_vars)"""return the next variable to split""return select(iter_vars def partition_domain(dom)"""partitions domain dom into two ""split len(dom/ dom set(list(dom)[:split]dom dom dom return dom dom the domains are implemented as dictionary that maps each variables to its domain assigning value in python has side effects which we want to avoid copy with assign takes copy of the domains dictionaryperhaps allowing for new domain for variable it creates copy of the csp with an (optionalassignment of new domain to variable only the domains are copied cspconsistency py -(continued def copy_with_assign(domainsvar=nonenew_domain={truefalse})"""create copy of the domains with an assignment var=new_domain if var==none then it is just copy ""newdoms domains copy(if var is not nonenewdoms[varnew_domain return newdoms cspconsistency py -(continued def select(iterable)"""select an element of iterable returns none if there is no such element this implementation just picks the first element for many of the useswhich element is selected does not affect correctnessbut may affect efficiency ""for in iterablereturn returns first element found exercise implement of solve all that is like solve one but returns the set of all solutions exercise implement solve enum that enumerates the solutions it should use python' yield (and perhaps yield fromunit testversion june