removed 1st edition code

17-it-generator/tree/step1/tree.py

@@ -1,10 +0,0 @@
-def tree(cls):
-    yield cls.__name__, 0                        # <1>
-    for sub_cls in cls.__subclasses__():         # <2>
-        yield sub_cls.__name__, 1                # <3>
-
-
-if __name__ == '__main__':
-    for cls_name, level in tree(BaseException):
-        indent = ' ' * 4 * level                 # <4>
-        print(f'{indent}{cls_name}')