Anexen / convertible

Convertible

Value-to-value conversion in Python.

Usage

Convertible

First, let's create a model for conversion. The model can be any class.

For convenience, let's take dataclass:

from dataclasses import dataclass
from convertible import Convertible

@dataclass
class User(Convertible):
    name: str
    age: int

Now User has conversion methods try_from and try_into. But we haven't implemented any converter. Let's do this.

From Converter

from typing import Tuple
from convertible import From

class UserFromTuple(From[tuple[str, int], User]):
    def try_from(self, value: tuple[str, int]) -> User:
        return User(name=value[0], age=value[1])

Now we can instantiate User from tuple:

user = User.try_from(("John", 23))
assert user.age == 23

Into Converter

We can convert user into another type. Let's define the converter:

# note that User is now the first parameter:
class UserIntoDict(From[User, dict]):
    def try_from(self, user: User) -> dict:
        return {
            "username": user.name,
            "age": user.age
        }

data = user.try_into(dict)
assert data["username"] == user.name

Cross conversion

Implementing From for two Convertible classes automatically provides the second Convertible with an implementation for try_into:

@dataclass
class Admin(Convertible):
    name: str


class AdminFromUser(From[User, Admin]):
    def try_from(self, user: User) -> Admin:
        return Admin(name=user.name)


# these are equivalent
assert user.try_into(Admin) == Admin.try_from(user)

Manual converter registration

You may need to define converters for types that are not Convertible. This can be done using the register_converter function:

class IntFromString:
    def try_from(self, value: str) -> int:
        return int(value)

From[int, str].register_converter(IntFromString)

value = From[int, str].try_from("123")
assert value == 123