ch17: update from book draft

17-it-generator/tree/step0/test_tree.py

@@ -0,0 +1,8 @@
+from tree import tree
+
+
+def test_1_level():
+    class One: pass
+    expected = ['One']
+    result = list(tree(One))
+    assert expected == result 

17-it-generator/tree/step0/tree.py

@@ -0,0 +1,7 @@
+def tree(cls):
+    yield cls.__name__
+
+
+if __name__ == '__main__':
+    for cls_name in tree(BaseException):
+        print(cls_name)