diff --git a/python/transition.py b/python/transition.py
new file mode 100644
index 0000000000000000000000000000000000000000..27500f962fb338e7c999e2a4466e68d628b4436e
--- /dev/null
+++ b/python/transition.py
@@ -0,0 +1,17 @@
+    def store_transition(self, s, a, r, s_):
+        transition = []
+        transition.append(s)
+        transition.append(a)
+        transition.append(r)
+        transition.append(s_)
+        transitionn = np.array(transition, dtype=object)
+        if self.prioritized:    # prioritized replay
+            #transition = np.hstack((s, [a, r], s_))
+            self.memory.store(transitionn)    # have high priority for newly arrived transition
+        else:       # random replay
+            if not hasattr(self, 'memory_counter'):
+                self.memory_counter = 0
+            #transition = np.hstack((s, [a, r], s_))
+            index = self.memory_counter % self.memory_size
+            self.memory[index, :] = transitionn
+            self.memory_counter += 1
\ No newline at end of file