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control/guido/guido3.py

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+"""
+Exemplo adaptado da mensagem do Guido van Rossum em:
+https://groups.google.com/forum/#!msg/python-tulip/bmphRrryuFk/aB45sEJUomYJ
+http://bit.ly/yieldfrom
+
+    >>> principal_susto(ger2())
+    OK
+    Bu!
+
+Visualização no PythonTutor: http://goo.gl/QXzQHS
+
+"""
+
+def ger1():
+    try:
+        val = yield 'OK'
+    except RuntimeError as exc:
+        print(exc)
+    else:
+        print(val)
+    yield  # para evitar o StopIteration
+
+
+def ger2():
+    yield from ger1()
+
+
+def principal_susto(g):
+    print(next(g))
+    g.throw(RuntimeError('Bu!'))
+
+
+# auto-teste
+import doctest
+doctest.testmod()