The following example is given by the documentation:

In the statement for X in Y, Y must be an iterator or some object for which iter() can create an iterator. These two statements are equivalent:

for i in iter(obj):
    print(i)

for i in obj:
    print(i)

According to this same source,

Behind the scenes, the for statement calls iter() on the container object. The function returns an iterator object that defines the method __next__() which accesses elements in the container one at a time. When there are no more elements, __next__() raises a StopIteration exception which tells the for loop to terminate.

Considering both cases, when Y is an iterator or some object for which iter() can create an iterator,

• if Y is an iterable (has an iter() method), the for statement calls this method and returns an iterator whose next() method is used to iterate through each element of Y. I assume this is the second example above.
• if Y is an iterator (has both an iter() and next() method), the for statement still calls the iter() method, but because it's an iterator, it returns itself, and the next() method is called as usual. I assume this is the first example above.

My question being, is my line of reasoning correct? I don't mind if you point out any misuse of a definition.

CodePudding user response：

See https://docs.python.org/3/library/stdtypes.html#typeiter.

iterator.__iter__()

Return the iterator object itself. This is required to allow both containers and iterators to be used with the for and in statements. This method corresponds to the tp_iter slot of the type structure for Python objects in the Python/C API.