advanced patterns when using Python 3.10 with dataclasses and default factory
I'm having trouble with I'm having trouble with I've been working on this all day and I'm integrating two systems and I've been banging my head against this for hours..... I tried several approaches but none seem to work... Hey everyone, I'm running into an issue that's driving me crazy. I'm working with an scenario with a dataclass in Python 3.10 where I'm using a default factory for a field, but it seems to be causing unexpected behavior when I instantiate the class multiple times. Here’s the relevant code snippet: ```python from dataclasses import dataclass, field from typing import List @dataclass class MyClass: items: List[int] = field(default_factory=list) instance1 = MyClass() instance2 = MyClass() instance1.items.append(1) print(instance1.items) # Expected: [1] print(instance2.items) # Expected: [] ``` I expect `instance2.items` to be an empty list, but instead it seems to reference the same list as `instance1.items`. When I run the above code, I get this output: ``` [1] [1] ``` I've read that using `field(default_factory=list)` should ensure that each instance of `MyClass` has its own separate list. I also tried using `items: List[int] = field(default=[])`, but that leads to the same scenario. I've verified that I’m not accidentally modifying the list in other parts of my code. Is there a mistake in how I'm using the default factory, or is this a known scenario in Python 3.10? What’s the best practice for ensuring separate instances of mutable default fields in dataclasses? My development environment is Linux. Thanks in advance! This is part of a larger service I'm building. Hoping someone can shed some light on this. Is there a simpler solution I'm overlooking? I'm working in a Linux environment. Any advice would be much appreciated. Hoping someone can shed some light on this.