Precomputes transition probabilities for each node.

def _precompute_probabilities(self):
        """
        Precomputes transition probabilities for each node.
        """

        d_graph = self.d_graph
        first_travel_done = set()

        nodes_generator = self.graph.nodes() if self.quiet \
            else tqdm(self.graph.nodes(), desc='Computing transition probabilities')

        for source in nodes_generator:

            # Init probabilities dict for first travel
            if self.PROBABILITIES_KEY not in d_graph[source]:
                d_graph[source][self.PROBABILITIES_KEY] = dict()

            for current_node in self.graph.neighbors(source):

                # Init probabilities dict
                if self.PROBABILITIES_KEY not in d_graph[current_node]:
                    d_graph[current_node][self.PROBABILITIES_KEY] = dict()

                unnormalized_weights = list()
                first_travel_weights = list()
                d_neighbors = list()

                # Calculate unnormalized weights
                for destination in self.graph.neighbors(current_node):

                    p = self.sampling_strategy[current_node].get(self.P_KEY,
                                                                 self.p) if current_node in self.sampling_strategy else self.p
                    q = self.sampling_strategy[current_node].get(self.Q_KEY,
                                                                 self.q) if current_node in self.sampling_strategy else self.q

                    if destination == source:  # Backwards probability
                        ss_weight = self.graph[current_node][destination].get(self.weight_key, 1) * 1 / p
                    elif destination in self.graph[source]:  # If the neighbor is connected to the source
                        ss_weight = self.graph[current_node][destination].get(self.weight_key, 1)
                    else:
                        ss_weight = self.graph[current_node][destination].get(self.weight_key, 1) * 1 / q

                    # Assign the unnormalized sampling strategy weight, normalize during random walk
                    unnormalized_weights.append(ss_weight)
                    if current_node not in first_travel_done:
                        first_travel_weights.append(self.graph[current_node][destination].get(self.weight_key, 1))
                    d_neighbors.append(destination)

                # Normalize
                unnormalized_weights = np.array(unnormalized_weights)
                d_graph[current_node][self.PROBABILITIES_KEY][
                    source] = unnormalized_weights / unnormalized_weights.sum()

                if current_node not in first_travel_done:
                    unnormalized_weights = np.array(first_travel_weights)
                    d_graph[current_node][self.FIRST_TRAVEL_KEY] = unnormalized_weights / unnormalized_weights.sum()
                    first_travel_done.add(current_node)

                # Save neighbors
                d_graph[current_node][self.NEIGHBORS_KEY] = d_neighbors