Why does a yield from inside __next__() return generator object?

Question

I am using yield to return the next value in the __next__() function in my class. However it does not return the next value, it returns the generator object.

I am trying to better understand iterators and yield. I might be doing it in the wrong way.

Have a look.

class MyString:
    def __init__(self,s):
        self.s=s

    def __iter__(self):
        return self

    def __next__(self):
        for i in range(len(self.s)):
            yield(self.s[i])

r=MyString("abc")
i=iter(r)
print(next(i))

This returns:

generator object __next__ at 0x032C05A0

Answer 1

next pretty much just calls __next__() in this case. Calling __next__ on your object will start the generator and return it (no magic is done at this point).

---

In this case, you might be able to get away with not defining __next__ at all:

class MyString:
    def __init__(self,s):
        self.s=s

    def __iter__(self):
        for i in range(len(self.s)):
            yield(self.s[i])
        # Or...
        # for item in self.s:
        #     yield item

If you wanted to use __iter__ and __next__ (to define an iterator rather than simply making an iterable), you'd probably want to do something like this:

class MyString:
    def __init__(self,s):
        self.s = s
        self._ix = None

    def __iter__(self):
        return self

    def __next__(self):
        if self._ix is None:
            self._ix = 0

        try:
            item = self.s[self._ix]
        except IndexError:
            # Possibly reset `self._ix`?
            raise StopIteration
        self._ix += 1
        return item