从用户代码中引发的异常触发生成器中的 except 子句

Question

我有一系列嵌套的生成器，如果用户代码中发生异常，我想从第一个生成器知道，为了举例，考虑下面的代码：

#############################################################################
def generator():
    try:
        for i in (1, 2, 3, 4, 5, 6):
            print(f"Generator: {i}.")
            yield i
    except:
        print("Exception handled in generator")
        raise

#############################################################################
def intermediary_generator():
    try:
        gen = generator()
        while i := gen.send(None):
            print(f"Intermediary generator: {i}.")
            yield i
    except StopIteration:
        pass
    except:
        print ("Exception handled in intermediary generator")
        raise

############################################################################
user_code_generator = intermediary_generator()
try:
    while i := user_code_generator.send(None):
        print(f"User code generator: {i}.")
        if i == 4:
            raise Exception("The exception in the user code")
except StopIteration:
    pass
except:
    print("Exception handled in user code generator")
    raise

我需要用户代码中的异常向下传播到中间生成器和主生成器，我期望根据打印语句出现以下顺序：

Exception handled in generator
Exception handled in intermediary generator
Exception handled in user code generator

但是如果我执行上面的代码，我没有看到在生成器或中间生成器中处理的异常。

Answer 1

我想我会回答我自己的问题，生成器的 throw 方法正是我需要的，它将用户代码中的异常传播到主生成器。

#############################################################################
def generator():
    try:
        for i in (1, 2, 3, 4, 5, 6):
            print(f"Generator: {i}.")
            yield i
    except:
        print("Exception handled in generator")
        raise

#############################################################################
def intermediary_generator():
    try:
        gen = generator()
        while i := gen.send(None):
            print(f"Intermediary generator: {i}.")
            yield i
    except StopIteration:
        print("Stop iteration in intermediary generator")
    except Exception as exc:
        print ("Exception handled in intermediary generator")
        gen.throw(exc)
        raise

############################################################################
user_code_generator = intermediary_generator()
try:
    while i := user_code_generator.send(None):
        print(f"User code generator: {i}.")
        if i == 4:
            raise Exception("The exception in the user code")
except StopIteration:
    pass
except Exception as exc:
    print("Exception handled in user code generator")
    user_code_generator.throw(exc)
    raise

并且输出：

Generator: 1.
Intermediary generator: 1.
User code generator: 1.
Generator: 2.
Intermediary generator: 2.
User code generator: 2.
Generator: 3.
Intermediary generator: 3.
User code generator: 3.
Generator: 4.
Intermediary generator: 4.
User code generator: 4.
Exception handled in user code generator
Exception handled in intermediary generator
Exception handled in generator
Traceback (most recent call last):
  File "<string>", line 39, in <module>
  File "<string>", line 25, in intermediary_generator
  File "<string>", line 9, in generator
  File "<string>", line 20, in intermediary_generator
  File "<string>", line 34, in <module>
Exception: The exception in the user code

从用户代码中引发的异常触发生成器中的 except 子句

Trigger except clause in generator from exception raised in user code

python

generator

coroutine

yield

yield-from