Add support to attributes without default values

[miikargh]

Problem

yaml-data-class-config doesn't currently support attributes without default values.

Cause

The attribute FILE_PATH in config.py that does not have a default value causes the error.

Possible solution

Remove the FILE_PATH attribute or add it after the config.yml is loaded so that it doesn't cause problems with mypy.

Example

config.yml:

property_a: 1
property_b: '2'

example.py:

from dataclasses import dataclass, field
from yamldataclassconfig.config import YamlDataClassConfig


@dataclass
class Config(YamlDataClassConfig):
    property_a: int
    property_b: str

Running mypy example.py throws the following errors:

problem.py:7: error: Attributes without a default cannot follow attributes with one
problem.py:8: error: Attributes without a default cannot follow attributes with one
Found 2 errors in 1 file (checked 1 source file)

One can go around this problem by adding Union[None, <type>] to every attribute but this is not ideal since one might want to have attributes that throw error if no value is provided.

Environment

• Ubuntu 20.04.1 LTS x86_64
• mypy==0.782
• python==3.8.5

Thanks for the great library by the way!

[yukihiko-shinoda]

Hi, thanks for your feedback!

I deployed new version 1.4.0, would you check it ?
FILE_PATH was already specified as field(init=False).

cf. dataclasses.field | dataclasses — Data Classes — Python 3.8.5 documentation

However, mypy seems to not check it if its definition is return value of method.
I checked it recovered by this update.
163532d

config.yml:

property_a: 1
property_b: '2'

test.py:

from dataclasses import dataclass
from yamldataclassconfig.config import YamlDataClassConfig

@dataclass
class Config(YamlDataClassConfig):
    property_a: int
    property_b: str


CONFIG: Config = Config(0, "1")
CONFIG.load()
print(CONFIG.property_a)
print(CONFIG.property_b)

Result:

$ pipenv run python test.py
1
2
$ pipenv run mypy test.py
Success: no issues found in 1 source file

[miikargh]

Seems to work well after updating to yamldataclassconfig==1.4.0. Thanks a bunch!