remapper 1.0.2

Transform objects to and from similar structural mappings.

remapper

Transform objects to and from similar structural mappings. Useful for translating between sources of truth and presentational models of data.

Supports Python 3.8+. No dependencies.

Installation

$ pdm add remapper
# or
$ python -m pip install --user remapper

Usage

The examples below use dataclasses because they're easy, but remap works with any destination type that exposes attributes via its __init__.

A trivial example for remap is converting one dataclass into another without having to manually pass attributes:

from dataclasses import dataclass

from remapper import remap


@dataclass
class Source:
    a: int
    b: int
    c: int


@dataclass
class Destination:
    a: int
    b: int
    c: int


dest = remap(Source(a=1, b=2, c=3), Destination)
# >> Destination(a=1, b=2, c=3)

A more useful example would be in mapping an internal database model to an externally-facing dataclass:

from dataclasses import dataclass

from remapper import remap
from sqlalchemy.orm import DeclarativeBase, Mapped, MappedAsDataclass, mapped_column


class Base(DeclarativeBase, MappedAsDataclass):
    pass


class Source(Base):
    id: Mapped[int] = mapped_column(init=False, primary_key=True)

    a: Mapped[int]
    b: Mapped[int]
    c: Mapped[int]


@dataclass
class Destination:
    a: int
    b: int
    c: int

    @property
    def d(self) -> int:
        return self.a + self.b + self.c


source = Source(a=1, b=2, c=3)
await session.commit(source)

dest = remap(source, Destination)
dest.d
# >> 6

Overrides

There's a non-zero chance that a destination may require more data than available on a source. In those cases, you can manually provide values via the overrides keyword argument. Values in overrides will take precedence over values on the source:

from dataclasses import dataclass

from remapper import remap


@dataclass
class Source:
    a: int
    b: int


@dataclass
class Destination:
    a: int
    b: int
    c: int


dest = remap(Source(a=1, b=2), Destination, overrides={"b": 0, "c": 3})
# >> Destination(a=1, b=0, c=3)

Defaults

If a destination defines more attributes than available on a source, but the destination has default values for those additional attributes, you don't need to supply overrides:

from dataclasses import dataclass

from remapper import remap


@dataclass
class Source:
    a: int
    b: int


@dataclass
class Destination:
    a: int
    b: int
    c: int = 3


dest = remap(Source(a=1, b=2), Destination)
# >> Destination(a=1, b=2, c=3)

Nested Types

Some complex sources may have attributes that themselves need to be converted. Rather than remapping in several steps, you can use the nested_types keyword argument to specify inner types of the destination attributes:

from dataclasses import dataclass

from remapper import remap


@dataclass
class Source:
    b: int


@dataclass
class Destination:
    b: int


@dataclass
class ParentSource:
    a: int
    child: Source


@dataclass
class ParentDestination:
    a: int
    child: Destination


## this works but is kind of clunky
source = ParentSource(a=1, child=Source(b=1))
dest_child = remap(source.child, Destination)
dest = remap(source, ParentDestination, overrides={"child": dest_child})
# >> ParentDestination(a=1,child=Destination(b=1))

## so use this instead
dest = remap(
    ParentSource(a=1, child=Source(b=1)),
    ParentDestination,
    nested_types={"child": Destination},
)
# >> ParentDestination(a=1,child=Destination(b=1))

License

This software is licensed under the BSD 3-Clause Clear License.