desert fails on recursive type hints #88
Description
Given a definition of a binary tree type hint BTREE = Union[LEAF, Tuple['BTREE', 'BTREE']], this cause desert schema to end up in an indefinite loop in lib\typing.py. Given that it is stuck in a loop in stdlib, I am not sure if this is a desert issue vs a typing issue or if typing wasn't really designed for recursive type hints like this in the first place.
from typing import Optional, Union, Tuple
import desert
import attr
# Can be any type
LEAF = str
# Binary tree definition
BTREE = Union[LEAF, Tuple['BTREE', 'BTREE']]
def test_btree():
@attr.s(slots=True)
class A:
x: BTREE = attr.ib(default='leaf')
a = A()
schema = desert.schema(A)
d = schema.dump(a)Results in
Traceback (most recent call last):
File "C:\sveinse\tests\test_tree.py", line 19, in test_btree
schema = desert.schema(A)
File "c:\sveinse\venv\lib\site-packages\desert\__init__.py", line 24, in schema
return desert._make.class_schema(cls, meta=meta)(many=many)
File "c:\sveinse\venv\lib\site-packages\desert\_make.py", line 124, in class_schema
field.metadata,
File "c:\sveinse\venv\lib\site-packages\desert\_make.py", line 225, in field_for_schema
if not field and typ in _native_to_marshmallow:
File "C:\Users\sveinse\AppData\Local\Programs\Python\Python37-32\lib\typing.py", line 666, in __hash__
return hash((Union, frozenset(self.__args__)))
File "C:\Users\sveinse\AppData\Local\Programs\Python\Python37-32\lib\typing.py", line 667, in __hash__
return hash((self.__origin__, self.__args__))
File "C:\Users\sveinse\AppData\Local\Programs\Python\Python37-32\lib\typing.py", line 666, in __hash__
return hash((Union, frozenset(self.__args__)))
.... and forever.