2025-09-10:仓库迁移

4.迭代器与生成器/5.反向迭代.py

@@ -0,0 +1,31 @@
+
+
+if __name__ == "__main__":
+    a = [1, 2, 3, 4]
+    # python自带的reversed函数搞定了反向迭代，其本质时调用了__reversed__方法
+    for i in reversed(a):
+        print(i)
+
+    for i in a.__reversed__():
+        print(i)
+
+    # 如果想要实现类的反向迭代，可以在实现__iter__()方法的同时搞一个__reversed__()方法
+    class Countdown:
+        def __init__(self, start):
+            self.start = start
+
+        def __iter__(self):
+            n = self.start
+            while n > 1:
+                yield n
+                n -= 1
+
+        def __reversed__(self):
+            n = 1
+            while n <= self.start:
+                yield n
+                n += 1
+
+    a = Countdown(10)
+    for i in reversed(a):
+        print(i)