vars is set of variables factors is set of factors ""def __init__(selftitlevariables=nonefactors=none)self title title self variables variables self factors factors belief network (also known as bayesian networkis graphical model where all of the factors are conditional probabilitiesand every variable has conditional probability of it given its parents this only checks the first conditionand builds some useful data structures probgraphicalmodels py -(continued class beliefnetwork(graphicalmodel)"""the class of belief networks "" def __init__(selftitlevariablesfactors)"""vars is set of variables factors is set of factors all of the factors are instances of cpd ( prob""graphicalmodel __init__(selftitlevariablesfactorsassert all(isinstance( ,cpdfor in factorsself var cpt { child: for in factorsself var parents { child: parents for in factorsself children { :[for in self variablesfor in self var parentsfor par in self var parents[ ]self children[parappend(vself topological_sort_saved none the following creates topological sort of the nodeswhere the parents of node come before the node in the resulting order this is based on kahn' algorithm from probgraphicalmodels py -(continued def topological_sort(self)"""creates topological ordering of variables such that the parents of node are before the node ""if self topological_sort_savedreturn self topological_sort_saved next_vars { for in self var parents if not self var parents[nself display( ,'topological_sortnext_vars',next_varstop_order=[while next_varsvar next_vars pop(version june