python - 发电机是可调用的吗？哪个是发电机？

Question

A generator is simply a function which returns an object on which you can call next, such that for every call it returns some value, until it raises a StopIteration exception, signaling that all values have been generated. Such an object is called an iterator.

>>> def myGen(n):
...     yield n
...     yield n + 1
... 
>>> g = myGen(6)

我引用自 Understanding Generators in Python?

这是我想弄清楚的:

1. 哪个是生成器？ myGen或 myGen(6) ？

   根据上面的引述，我认为生成器应该是myGen .和 myGen(6)是返回的迭代器对象。但我真的不确定。

2. 当我尝试这样做时:

   >>> type(myGen)
   <type 'function'>
   >>> type(g)         # <1>this is confusing me.
   <type 'generator'>  
   >>> callable(g)     # <2> g is not callable.  
   False               
   >>> callable(myGen)
   True
   >>> g is iter(g)    # <3> so g should an iterable and an iterator 
   True                # at the same time. And it will be passed as an argument
   >>> for i in g:     # to built-in function `next()` in a "for...in..." loop.
           print i     # (is that correct?)
   
   6
   7     
   

因此，根据 <1>和 <2> , g的类型是“发电机”，它是不可调用的。但是generators are callable, and calling a generator gets you an iterator object这是怎么回事？

当我在寻找答案时，我遇到了 Every time you define a function python creates a callable object.

那么，我可以这样说吗？ 当函数 myGen已定义，myGen是一个引用可调用对象的名称，该对象是具有 __call__ 的类的实例方法。在这种情况下，myGen是一个发电机，myGen(6)是 myGen 时返回的迭代器叫做。

但为什么 type(g)返回 <type 'generator'>在所有？这返回了 iterator因为没有return，我觉得这件事也很可疑函数中的语句。

不就是Functions always return something (at least None , when no return-statement was reached during execution and the end of the function is reached)吗？

Answer 1

不幸的是，术语令人困惑，因为“生成器”经常用于指代函数或返回的迭代器，以至于很难说哪一种用法更正确。 documentation of the yield statement说

The yield statement is only used when defining a generator function, and is only used in the body of the generator function. Using a yield statement in a function definition is sufficient to cause that definition to create a generator function instead of a normal function.

When a generator function is called, it returns an iterator known as a generator iterator, or more commonly, a generator.

original PEP introducing the concept说

Note that when the intent is clear from context, the unqualified name "generator" may be used to refer either to a generator-function or a generator-iterator.

如果要明确区分，函数用“generator function”，迭代器用“generator iterator”。