[英]How can I tell whether a generator was just-started?
I'd like a function, is_just_started
, which behaves like the following: 我想要一个函数
is_just_started
,其行为类似于以下内容:
>>> 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
How can I implement this function? 我该如何实现这个功能?
I looked at the .gi_running
attribute but it appears to be used for something else. 我查看了
.gi_running
属性,但它似乎用于其他东西。
If I know the first value that needs to be sent into the generator, I can do something like this: 如果我知道需要发送到生成器的第一个值,我可以这样做:
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
However, this seems abhorrent. 然而,这似乎令人憎恶。
This only works in Python 3.2+: 这仅适用于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'
So, the requested function is: 因此,请求的功能是:
import inspect
def is_just_started(gen):
return inspect.getgeneratorstate(gen) == inspect.GEN_CREATED:
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". 出于好奇,我调查了CPython以弄清楚它是如何确定的......显然它看着
generator.gi_frame.f_lasti
,它是“字节码中最后一次尝试指令的索引”。 If it's -1
then it hasn't started yet. 如果它是
-1
那么它还没有开始。
Here's a py2 version: 这是一个py2版本:
def is_just_started(gen):
return gen.gi_frame is not None and gen.gi_frame.f_lasti == -1
Make a new generator which simply yields from your generator of interest. 制造一台新的发电机,只需从您感兴趣的发电机中产生。 It sets a flag once the first value has been consumed .
一旦消耗了第一个值,它就会设置一个标志 。 Afterwards, it can simply use
yield from
for the rest of the items. 之后,它可以简单地使用其他项目的
yield from
。
Use the substitute generator as a drop in replacement for the generator you're interested in monitoring the "is_just_started" state. 使用替代生成器代替您有兴趣监视“is_just_started”状态的生成器。
This technique is non-intrusive, and can be used even on generators for which you have no control over the source code. 此技术是非侵入式的,甚至可以在您无法控制源代码的生成器上使用。
You may create a iterator and set the flag as the instance property to iterator class as: 您可以创建一个迭代器并将标志作为实例属性设置为迭代器类,如下所示:
class gen(object):
def __init__(self, n):
self.n = n
self.num, self.nums = 0, []
self.is_just_started = True # Your flag
def __iter__(self):
return self
# Python 3 compatibility
def __next__(self):
return self.next()
def next(self):
self.is_just_started = False # Reset flag with next
if self.num < self.n:
cur, self.num = self.num, self.num+1
return cur
else:
raise StopIteration()
And your value check function would be like: 你的价值检查功能如下:
def is_just_started(my_generator):
return my_generator.is_just_started
Sample run: 样品运行:
>>> a = gen(2)
>>> 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>
File "<stdin>", line 19, in next
StopIteration
To know the difference between iterator and generator , check Difference between Python's Generators and Iterators 要了解迭代器和生成器之间的区别,请检查Python的生成器和迭代器之间的差异
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