如何判断发电机是否刚刚启动? [英] How can I tell whether a generator was just-started?

问题描述

我想要一个功能is_just_started，其功能如下:

I'd like a function, is_just_started, which behaves like the following:

>>> def gen(): yield 0; yield 1
>>> a = gen()
>>> is_just_started(a) 
True
>>> next(a)
0
>>> is_just_started(a) 
False
>>> next(a)
1
>>> is_just_started(a) 
False
>>> next(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration
>>> is_just_started(a)
False

如何实现此功能?

我查看了.gi_running属性，但该属性似乎用于其他用途.

I looked at the .gi_running attribute but it appears to be used for something else.

如果我知道需要发送到生成器的第一个值，则可以执行以下操作:

If I know the first value that needs to be sent into the generator, I can do something like this:

def safe_send(gen, a):
    try:
        return gen.send(a)
    except TypeError as e:
        if "just-started" in e.args[0]:
            gen.send(None)
            return gen.send(a)
        else:
            raise

但是，这似乎很可恶.

However, this seems abhorrent.

推荐答案

这仅适用于Python 3.2 +:

This only works in Python 3.2+:

>>> def gen(): yield 0; yield 1
... 
>>> a = gen()
>>> import inspect
>>> inspect.getgeneratorstate(a)
'GEN_CREATED'
>>> next(a)
0
>>> inspect.getgeneratorstate(a)
'GEN_SUSPENDED'
>>> next(a)
1
>>> inspect.getgeneratorstate(a)
'GEN_SUSPENDED'
>>> next(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration
>>> inspect.getgeneratorstate(a)
'GEN_CLOSED'

因此，请求的功能是:

import inspect

def is_just_started(gen):
    return inspect.getgeneratorstate(gen) == inspect.GEN_CREATED:

出于好奇，我调查了CPython以弄清它是如何确定的……显然，它查看的是generator.gi_frame.f_lasti，它是字节码中最后一次尝试执行的指令的索引".如果它是-1，则尚未启动.

Out of curiosity, I looked into CPython to figure out how it was determining this... Apparently it looks at generator.gi_frame.f_lasti which is the "index of last attempted instruction in bytecode". If it's -1 then it hasn't started yet.

这是py2版本:

def is_just_started(gen):
    return gen.gi_frame is not None and gen.gi_frame.f_lasti == -1

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