This subsection describes the methods of a generator iterator. They can be used to control the execution of a generator function.

Note that calling any of the generator methods below when the generator is already executing raises a ValueError exception.

class generator

generator.next()

Starts the execution of a generator function or resumes it at the last executed 

yield expression. When a generator function is resumed with a next() method, the current yield expression always evaluates to None. The execution then continues to the next yield expression, where the generator is suspended again, and the value of the expression_list is returned to next()‘s caller. If the generator exits without yielding another value, a 

StopIteration exception is raised.

★ 開始執行生成器方法或喚醒上一次執行 yield 表示式後被掛起的生成器。當一個生成器方法被用 next() 方法恢復時，當前的 yield 表示式總且一定為 None。方法繼續執行，直到下一個 yield 表示式，方法再次被掛起。返回值被呼叫 next() 的 caller 返回。如果生成器返回時沒有yield一個值，會引發 StopIteration 異常。

generator.send(value)

Resumes the execution and “sends” a value into the generator function. The value

 argument becomes the result of the current yield expression. The send() method returns the next value yielded by the generator, or raises StopIteration if the generator exits without yielding another value. When send() is called to start the generator, it must be called with None as the argument, because there is no yield expression that could receive the value.

★ 恢復方法的執行並給方法 sends 一個值。引數value 成為當前 yield 的結果。send()方法返回下一個被生成器 yield 的值，或者當方法沒有yield 一個值並且退出時，引起一個 StopIteration 異常。當用 send() 方法來第一次呼叫方法時，引數必須為 None ，因為沒有 yield 表示式能夠接受這個引數。

generator.throw(type[, value[, traceback]])

Raises an exception of type type at the point where generator was paused, and returns the next value yielded by the generator function. If the generator exits without yielding another value, a StopIteration exception is raised. If the generator function does not catch the passed-in exception, or raises a different exception, then that exception propagates to the caller.

★ 引發一個給定的異常，返回下一個yield的值。如果生成器沒有 yield 一個值，會引發 StopIteration 異常。如果生成器沒有捕捉給定得異常或引發了不同於引數裡給定異常的異常，這個異常會被拋給 caller。

generator.close()

Raises a GeneratorExit at the point where the generator function was paused. If the generator function then raises StopIteration (by exiting normally, or due to already being closed) or GeneratorExit (by not catching the exception), close returns to its caller. If the generator yields a value, a RuntimeError is raised. If the generator raises any other exception, it is propagated to the caller. close() does nothing if the generator has already exited due to an exception or normal exit.

Here is a simple example that demonstrates the behavior of generators and generator functions:

>>> def echo(value=None):
...     print "Execution starts when 'next()' is called for the first time."
...     try:
...         while True:
...             try:
...                 value = (yield value)
...             except Exception, e:
...                 value = e
...     finally:
...         print "Don't forget to clean up when 'close()' is called."
...
>>> generator = echo(1)
>>> print generator.next()
Execution starts when 'next()' is called for the first time.
1
>>> print generator.next()
None
>>> print generator.send(2)
2
>>> generator.throw(TypeError, "spam")
TypeError('spam',)
>>> generator.close()
Don't forget to clean up when 'close()' is called.