Adds most dataclass features from Python versions after 3.7 to the excellent but long-since abandoned backport by Eric V. Smith (https://github.com/ericvsmith/dataclasses/).
For those of us still stuck writing Python for systems tied hard to the oldest LTS releases of Ubuntu and RedHat.
Matrix of backported and not-yet-backported features:
| Python version | Feature | Status |
|---|---|---|
| 3.8 | InitVar[T] generic syntax |
Backported |
| 3.8 | replace() handling of InitVar fields with defaults |
Backported |
| 3.10 | kw_only parameter and KW_ONLY sentinel |
Backported |
| 3.10 | match_args parameter (__match_args__ generation) |
Backported |
| 3.10 | slots parameter (__slots__ generation) |
Backported |
| 3.11 | weakref_slot parameter |
Backported |
| 3.11 | Frozen+slots pickling (__getstate__/__setstate__) |
Backported |
| 3.11 | Slots with init=False default fields (bpo-44649) |
Backported |
| 3.11–3.12 | fields() traceback improvements |
Backported |
| 3.11–3.12 | Mutable default value validation | Backported |
| 3.12 | Field named BUILTINS in frozen classes (gh-96151) |
Backported |
| 3.12 | Special underscore field names like _dflt_x (gh-98886) |
Backported |
| 3.12 | Inherited __dict__ slot handling |
Backported |
| 3.12–3.13 | Optimized __eq__ and __repr__ recursion guards |
Backported |
| 3.12 | asdict()/astuple() atomic-type fast paths (gh-91896) |
Backported |
| 3.13 | Single-exec method generation (_FuncBuilder, gh-107550) |
Backported |
| 3.13 | Non-frozen subclass of frozen: mutable attr set/delete | Backported |
| 3.14 | decorator parameter for make_dataclass() |
Backported |
| 3.12 | module parameter for make_dataclass() |
Not backported |
| 3.12 | defaultdict support in asdict()/astuple() |
Not backported |
| 3.13 | __replace__() method (copy.replace() support) |
Not backported |
Drop the single dataclasses.py file into your project (vendoring), or add it to
your Python path. It is a drop-in replacement for the standard library module and
can transparently replace the stdlib if running on a Python version that doesn't
support some feature you like.
Supports Python 3.6 and later from a single codebase — the only
version-sensitive code is the ClassVar detection, which adapts to the
typing internals of the running interpreter. The test suite runs in CI on
Python 3.6 through 3.13.
Note: don't mix this module with the stdlib dataclasses in the same class.
InitVar, Field, field() and the KW_ONLY sentinel are compared by
identity, so e.g. a stdlib InitVar annotation on a class decorated with this
module's @dataclass will not be recognized. Import everything from one module,
as in the example below.
try:
from dataclasses import dataclass, field, KW_ONLY
except ImportError:
from myproj.vendor.dataclasses import dataclass, field, KW_ONLY # type: ignore[no-redef]
@dataclass(slots=True, kw_only=True)
class Point:
x: float
y: float
z: float = 0.0@dataclass(
init=True, # 3.7
repr=True, # 3.7
eq=True, # 3.7
order=False, # 3.7
unsafe_hash=False, # 3.7
frozen=False, # 3.7
match_args=True, # 3.10
kw_only=False, # 3.10
slots=False, # 3.10
weakref_slot=False, # 3.11
)
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