Cannot use Literal from standard library in 3.8 #1026
Description
Bug
- OS: macOS
- Python version
import sys; print(sys.version): 3.8.0 - Pydantic version
import pydantic; print(pydantic.VERSION): 1.1.1
Annotating models with the built-in literal in Python 3.8 in the absence of typing_extensions does not work because is_literal_type only checks if Literal is available from typing_extensions. Please see the snippet below.
$ cat test.py
from typing import Literal
from pydantic import BaseModel
class Foo(BaseModel):
bar: Literal['']
print('ok!')
$ python3 test.py
Traceback (most recent call last):
File "test.py", line 5, in <module>
class Foo(BaseModel):
File "/Users/layday/code/instawow/.venvs/3.8/lib/python3.8/site-packages/pydantic/main.py", line 192, in __new__
fields[ann_name] = ModelField.infer(
File "/Users/layday/code/instawow/.venvs/3.8/lib/python3.8/site-packages/pydantic/fields.py", line 260, in infer
return cls(
File "/Users/layday/code/instawow/.venvs/3.8/lib/python3.8/site-packages/pydantic/fields.py", line 237, in __init__
self.prepare()
File "/Users/layday/code/instawow/.venvs/3.8/lib/python3.8/site-packages/pydantic/fields.py", line 307, in prepare
self._type_analysis()
File "/Users/layday/code/instawow/.venvs/3.8/lib/python3.8/site-packages/pydantic/fields.py", line 359, in _type_analysis
if issubclass(origin, Tuple): # type: ignore
File "/nix/store/mnl1njrv6g2jcs69kq0cy19766kcgc5n-python3-3.8.0/lib/python3.8/typing.py", line 771, in __subclasscheck__
return issubclass(cls, self.__origin__)
TypeError: issubclass() arg 1 must be a class
$ pip3 install typing_extensions
Collecting typing_extensions
Using cached https://files.pythonhosted.org/packages/03/92/705fe8aca27678e01bbdd7738173b8e7df0088a2202c80352f664630d638/typing_extensions-3.7.4.1-py3-none-any.whl
Installing collected packages: typing-extensions
Successfully installed typing-extensions-3.7.4.1
WARNING: You are using pip version 19.2.3, however version 19.3.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
$ python3 test.py
ok!