[Feature] Added changing priority queue task priority.

Author: exterkamp

structures/priority_queue.py

@@ -16,12 +16,21 @@ def add_task(self, task, priority=0):
             self.remove_task(task)
         count = next(self.counter)
         entry = [priority, count, task]
-        self.mapper [task] = entry
+        self.mapper[task] = entry
         heappush(self.pq, entry)
 
     def remove_task(self, task):
         entry = self.mapper.pop(task)
         entry[-1] = self.REMOVED
+    
+    def set_priority(self, task, priority=None):
+        if task in self.mapper:
+            entry = self.mapper.pop(task)
+
+            if not priority:
+                priority = min(0, entry[0] - 1)
+
+            self.add_task(entry[2], priority)
 
     def pop_task(self):
         while self.pq:

tests/test_priority_queue.py

@@ -21,4 +21,25 @@ def test_pq_simple(self):
         self.assertEqual('park at work', pq.pop_task())
 
         with self.assertRaises(KeyError):
-            pq.pop_task()
+            pq.pop_task()
+    
+    def test_set_priority(self):
+        pq = PriorityQueue()
+        pq.add_task('drive to work', 2)
+        pq.add_task('get keys')
+        pq.add_task('load car', 1)
+        pq.add_task('check gas', 1)
+        pq.add_task('turn on car', 1)
+        pq.add_task('park at work', 3)
+        pq.remove_task('load car')
+        pq.add_task('check gas', 1)
+
+        self.assertEqual('get keys', pq.pop_task())
+
+        pq.set_priority('park at work', 0)
+
+        self.assertEqual('park at work', pq.pop_task())
+
+        pq.set_priority('load car', 5)
+
+        self.assertEqual('turn on car', pq.pop_task())