Simple infinite iterator in Python

Question

a few days ago I started working in my friend's startup as junior Python developer, we are the only employees.

I have noticed he sometimes writes strange code. For example this:

@pytest.fixture
def create_user_model_test_data():
    positive_numbers_iterator = (
        lambda n: type("DeclarativeParametrizedNumbersInfiniteIterator", (), {
            "__iter__": lambda self: self,
            "__next__": staticmethod(
                (
                    lambda n:
                    (
                        lambda arg_dict:
                        lambda: (
                            arg_dict.update({"n": arg_dict["n"] + 1}) or arg_dict["n"] - 1,
                        )
                    )
                    ({"n": n})
                )
                (n)
            )
        })
        ()
    )
    positive_numbers_starting_from_zero_iterator = positive_numbers_iterator(0)
    # FIXME: dont know why python needs a while to iterate a sequence but anyways
    while "1":
        for n in next(map(next, [positive_numbers_starting_from_zero_iterator])):
            if n == 20: return
            create_user(name=f"user-{n}", role=["admin", "user"][n % 2])

I recommended changing it by this:

N = -1
def iterate_numbers():
    N += 1
    return N

However, he said it is impure, not declarative and can't be parametrized. I said it's not a problem and that the declarative ways is ugly, but he replied that Python is ugly, you can write a simple declarative infinite iterator in Haskell, and now is considering rewriting the entire project in Haskell. I love Python and want to learn it, I don't know Haskell nor want to learn.

Please, tell me how to write a simple declarative parametrized pure infinite numbers sequence in Python without mutating global variables, I don't want to learn Haskell, I need to convince him to stick with Python.

EDIT: Note that the iterator can be written in only 1 line of code, which is nice, but I have formated it so you can easily understand it

Note, your friends approach *uses mutation*: `arg_dict.update`. In any case, you just want `itertools.count` — juanpa.arrivillaga, Sep 21 '21 at 18:24
Note, your `iterate_numbers` function *is not an iterator at all* — juanpa.arrivillaga, Sep 21 '21 at 18:26
@juanpa.arrivillaga Yes, and the .update is part of the joke. Also, the create_user has side effects — Pablo, Sep 21 '21 at 18:28
@Pablo and `# FIXME: dont know why python needs a while to iterate a sequence but anyways` is crazy. — juanpa.arrivillaga, Sep 21 '21 at 18:28

Szabolcs · Answer 1 · 2021-09-21T18:25:35.233

3

This is a function which will return an infinite number generator. You can define the start as well.

def iterate_numbers(start=0):
    while True:
        yield start
        start += 1

edited Sep 21 '21 at 18:25

answered Sep 21 '21 at 18:21

Szabolcs

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3

but why? Just use `itertools.count` – juanpa.arrivillaga Sep 21 '21 at 18:25
2

I wanted to suggest that as well, however you do not learn from that, but sure you can use it after you understand how it works. – Szabolcs Sep 21 '21 at 18:30

Simple infinite iterator in Python

1 Answers1