rspec/rules/S2876/python/rule.adoc

The https://docs.python.org/3/library/stdtypes.html#iterator-types[iterator protocol] specifies that the ``++__iter__++`` method can only return an iterator, i.e. an object with a ``++__next__++`` and an ``++__iter__++`` method (because iterators are also iterable). Returning anything else than an iterator will raise a ``++TypeError++`` as soon as the iteration begins.


Note that https://docs.python.org/3/tutorial/classes.html#generators[generators] and https://docs.python.org/3/tutorial/classes.html#generator-expressions[generator expressions] have both ``++__next__++`` and ``++__iter__++`` methods generated automatically.


This rule raises an issue when the object returned by an ``++__iter__++`` method does not have a method ``++__next__++``.

== Noncompliant Code Example

----
class MyIterable:
    def __init__(self, values):
        self._values = values

    def __iter__(self):
        return None  # Noncompliant
----

== Compliant Solution

----
class MyIterable:
    def __init__(self, values):
        self._values = values

    def __iter__(self):
        return MyIterator(self._values)

class MyIterator:
    def __init__(self, values):
        self._values = values
        self._index = 0

    def __next__(self):
        if self._index >= len(self._values):
            raise StopIteration()
        value = self._values[self._index]
        self._index += 1
        return value

    def __iter__(self):
        return self
----

== See

* https://www.python.org/dev/peps/pep-0234/#python-api-specification[PEP 234 - Iterators]
* https://docs.python.org/3/library/stdtypes.html#iterator-types[Python documentation - Iterator Types]