rspec/rules/S3862/python/rule.adoc

For-in loops, https://docs.python.org/3/whatsnew/3.3.html#pep-380-syntax-for-delegating-to-a-subgenerator[``yield from``] and iterable unpacking only work with https://docs.python.org/3/glossary.html#term-iterable[iterable objects]. In order to be iterable, an object should have either an ``\_\_iter\_\_`` method or a ``\_\_getitem\_\_`` method implementing the https://docs.python.org/3/glossary.html#term-sequence[Sequence] semantic.

Note also that iterating over an https://docs.python.org/3/glossary.html#term-asynchronous-iterable[asynchronous iterable], i.e. an object having the ``\_\_aiter\_\_`` method, requires the use of https://docs.python.org/3/reference/compound_stmts.html#the-async-for-statement[``async for ... in``] instead of ``for ... in``.

This rule raises an issue when a non iterable object is used in a ``for-in`` loop, in a ``yield from`` or when it is unpacked.

== Noncompliant Code Example

----
class Empty:
    pass

empty = Empty()

for a in empty:  # Noncompliant
    print(a)

a, b, c = empty  # Noncompliant

print(*empty)  # Noncompliant

[1, 2, 3, *empty]  # Noncompliant

# yield from
def generator():
    yield from Empty()  # Noncompliant

# async generators
async def async_generator():
    yield 1

a, *rest = async_generator()  # Noncompliant
for a in async_generator():  # Noncompliant; "async" is missing before "for"
    print(a)
----

== Compliant Solution

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

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

my_iterable = MyIterable(range(10))

for a in my_iterable:
    print(a)

a, b, *c = my_iterable

print(*my_iterable)

[1, 2, 3, *my_iterable]

# yield from
def generator():
    yield from subgenerator()

def subgenerator():
    yield 1

# async generators
async def async_generator():
    yield 1

async for a in async_generator():
    print(a)
----

== 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]