dataclasses_python_3.12.py

#!/usr/bin/python3.12

from dataclasses import asdict, dataclass

@dataclass
class User:
    username: str
    skills: list[str]  # Expecting a list of strings...


if __name__ == "__main__":
    user = User(username="ivanleoncz", skills="Python")  # ...but got a string.
    print(user)
    print(asdict(user))

"""
$ ./dataclasses_python_3.12.py
User(username='ivanleoncz', skills='Python')
{'username': 'ivanleoncz', 'skills': 'Python'}
"""
#!/usr/bin/python3.12
from dataclasses import dataclass, field

@dataclass
class User:
    username: str
    skills: list[str] = field(default_factory=list)

    def validation(self) -> None:

        wrong_data_types = []
        for field in self.__dataclass_fields__.keys():
            """
            Inspecting __dataclass__fields, obtaining direct or original data type,
            verifying if field value had the expected data type.
            """
            data_type_detected = getattr(self.__dataclass_fields__[field].type, "__origin__",
                                         self.__dataclass_fields__[field].type)
            if not isinstance(getattr(self, field), data_type_detected):
                wrong_data_types.append(field)

        if wrong_data_types:
            raise AttributeError(f"data type violation detected: {wrong_data_types}")

    def __post_init__(self):
        self.validation()

if __name__ == "__main__":
    # username must be a str...
    user = User(username=123, skills=["docker", "aws", "azure"])

"""
$ ./dataclasses_instantiation_validation_python_3.12.py
Traceback (most recent call last):
  File "/tmp/test_2.py", line 30, in <module>
    user = User(username=123, skills=["docker", "aws", "azure"])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<string>", line 5, in __init__
  File "/tmp/test_2.py", line 26, in __post_init__
    self.validation()
  File "/tmp/test_2.py", line 23, in validation
    raise AttributeError(f"data type violation detected: {wrong_data_types}")
AttributeError: data type violation detected: ['username']
"""
#!/usr/bin/python3.12

from pydantic import BaseModel

class User(BaseModel):
    """
    Any wrong data type (e.g. 'int' instead of 'str' when creating an object of User (say "name"),
    would result in an exception like:

        ValidationError: 1 validation error for User
        name
    """
    id: int
    name: str


if __name__ == "__main__":

    external_data = {
        'id': 48,
        'name': 'jack62',
    }

    user = User(**external_data)
    print("name (before): ", user.name)

    # Instance variable changed to other data type, without any constraint...
    user.name = 123
    print("name (after):  ", user.name)


"""
$ ./pydantic_python_3.12.py
name (before):  jack62
name (after):   123
"""