[Feature Request] Support for Python 3.11

[zhiruiluo]

Feature requested

Is your feature request related to a problem? Please describe.
Add support for Python 3.11.
Python 3.11.1 is released at Dec. 6 2022.
ref: https://www.python.org/downloads/release/python-3111/

Python 3.11 support graph for the 360 most popular Python packages! https://pyreadiness.org/3.11/

Highlight:

• Python 3.11 is between 10-60% faster than Python 3.10. On average, we measured a 1.25x speedup on the standard benchmark suite.

Motivation

Python 3.11 is fast! And we enjoy speedup 😊!

Known issue

• Change field default mutability check, allowing only defaults which are hashable instead of any object which is not an instance of dict, list or set. (Contributed by Eric V. Smith in bpo-44674.) [ref]
• dataclass decorator requires nested dataclasses to use default_factory or make nested dataclasses hashable
• Many test cases using mutable default will fail
• get_help_text in TestSetup fail for nested dataclasses using default_factory
• test_mutable_field in test_utils.py will fail due to default_factory initialize a new object for the shared A everytime.
• examples using mutable default will fail in Python 3.11
• simple_parsing.decorator main will need to be modified.
• field_wrapper default value might be set by default_factory.

Error Example:

from dataclasses import dataclass

@dataclass
class A():
    arg_str: str = 'test'
    arg_int: int = 1
    arg_float: float = 0.5

@dataclass
class B():
    a: A = A()

def test_dataclass():
    B()

output:

ERROR test/python311/test_dataclass.py - ValueError: mutable default <class 'test.python311.test_dataclass.A'> for field a is not allowed: use default_factory

Passed Example:

from dataclasses import dataclass

@dataclass(eq=True,frozen=True)
class A():
    arg_str: str = 'test'
    arg_int: int = 1
    arg_float: float = 0.5

@dataclass
class B():
    a: A = A()

def test_dataclass():
    B()

Describe the solution you'd like

• Add test for Python 3.11 to CI
• Modify test cases and examples to comply the default mutable check
• Add docs for different usages in Python==3.11 and Python<=3.10
• Identify and fix related bugs

Describe alternatives you've considered

Additional context

[zhiruiluo]

Possible solution

We can pass dataclasses to the default_factory argument of field.

from dataclasses import dataclass, field

@dataclass()
class A():
    arg_str: str = 'test'
    arg_int: int = 1
    arg_float: float = 0.5

@dataclass
class B():
    # using lambda to initialize a user specified dataclass object
    a: A = field(default_factory=lambda: A(arg_str='hi'))

@dataclass
class C():
    # or pass a dataclass class direct to default_factory 
    a: A = field(default_factory=A)

def test_dataclass():
    B()
    C()

[lebrice]

This makes total sense. Will look into this as soon as I can. Thanks @zhiruiluo ! :)