I am writing a python class that acts as an immutable, infinite sequence.
The class does not use a generator to access this infinite sequence, rather it generates a value for an arbitrary index in the sequence according to an algorithm within the __getitem__ method.
I am curious what the best way to handle the __len__ method of such an object is. Ideally, I would just return float("inf") through __len__. However, the len() function that calls an object's __len__ method behind the scenes requires a somewhat specific value.
If __len__ is set to return float("inf") or decimal.Decimal("Infinity"), len() rejects it by raising a TypeError. It also rejects the value of "-1" which would imply that the sequence is infinite. Furthermore, when I tried using an infinity class that I happen to have written earlier that does in fact inherit from int, len() for whatever reason returned 0.
While it isn't really a major inconvenience to allow the value to just be "0", and while a class like this is very unusual, I am still curious to know, is there a good way to handle the length attribute of a class that is an infinite sequence?
__len__() must return a valid integer. Since you cannot, you should either not implement __len__(), if your sequences are always infinite, or raise a ValueError if you can sometimes give a meaningful length.