Source code
from __future__ import annotations
import abc
import contextlib
import enum
import itertools
import linecache
import sys
import types
import unicodedata
import weakref
from collections.abc import Callable, Mapping
from functools import cached_property
from typing import Any, NamedTuple, TypeVar
from . import _compat, _config, setters
from ._compat import (
PY_3_11_PLUS,
PY_3_13_PLUS,
_AnnotationExtractor,
_get_annotations,
_lazy_is_generator,
get_generic_base,
)
from .exceptions import (
DefaultAlreadySetError,
FrozenInstanceError,
NotAnAttrsClassError,
UnannotatedAttributeError,
)
class Attribute:
"""
*Read-only* representation of an attribute.
.. warning::
You should never instantiate this class yourself.
The class has *all* arguments of `attr.ib` (except for ``factory`` which is
only syntactic sugar for ``default=Factory(...)`` plus the following:
- ``name`` (`str`): The name of the attribute.
- ``alias`` (`str`): The __init__ parameter name of the attribute, after
any explicit overrides and default private-attribute-name handling.
- ``alias_is_default`` (`bool`): Whether the ``alias`` was automatically
generated (``True``) or explicitly provided by the user (``False``).
- ``inherited`` (`bool`): Whether or not that attribute has been inherited
from a base class.
- ``eq_key`` and ``order_key`` (`typing.Callable` or `None`): The
callables that are used for comparing and ordering objects by this
attribute, respectively. These are set by passing a callable to
`attr.ib`'s ``eq``, ``order``, or ``cmp`` arguments. See also
:ref:`comparison customization <custom-comparison>`.
Instances of this class are frequently used for introspection purposes
like:
- `fields` returns a tuple of them.
- Validators get them passed as the first argument.
- The :ref:`field transformer <transform-fields>` hook receives a list of
them.
- The ``alias`` property exposes the __init__ parameter name of the field,
with any overrides and default private-attribute handling applied.
.. versionadded:: 20.1.0 *inherited*
.. versionadded:: 20.1.0 *on_setattr*
.. versionchanged:: 20.2.0 *inherited* is not taken into account for
equality checks and hashing anymore.
.. versionadded:: 21.1.0 *eq_key* and *order_key*
.. versionadded:: 22.2.0 *alias*
.. versionadded:: 26.1.0 *alias_is_default*
For the full version history of the fields, see `attr.ib`.
"""
# These slots must NOT be reordered because we use them later for
# instantiation.
__slots__ = ( # noqa: RUF023
"name",
"default",
"validator",
"repr",
"eq",
"eq_key",
"order",
"order_key",
"hash",
"init",
"metadata",
"type",
"converter",
"kw_only",
"inherited",
"on_setattr",
"alias",
"alias_is_default",
)
def __init__(
self,
name,
default,
validator,
repr,
cmp, # XXX: unused, remove along with other cmp code.
hash,
init,
inherited,
metadata=None,
type=None,
converter=None,
kw_only=False,
eq=None,
eq_key=None,
order=None,
order_key=None,
on_setattr=None,
alias=None,
alias_is_default=None,
):
eq, eq_key, order, order_key = _determine_attrib_eq_order(
cmp, eq_key or eq, order_key or order, True
)
# Cache this descriptor here to speed things up later.
bound_setattr = _OBJ_SETATTR.__get__(self)
# Despite the big red warning, people *do* instantiate `Attribute`
# themselves.
bound_setattr("name", name)
bound_setattr("default", default)
bound_setattr("validator", validator)
bound_setattr("repr", repr)
bound_setattr("eq", eq)
bound_setattr("eq_key", eq_key)
bound_setattr("order", order)
bound_setattr("order_key", order_key)
bound_setattr("hash", hash)
bound_setattr("init", init)
bound_setattr("converter", converter)
bound_setattr(
"metadata",
(
types.MappingProxyType(dict(metadata)) # Shallow copy
if metadata
else _EMPTY_METADATA_SINGLETON
),
)
bound_setattr("type", type)
bound_setattr("kw_only", kw_only)
bound_setattr("inherited", inherited)
bound_setattr("on_setattr", on_setattr)
bound_setattr("alias", alias)
bound_setattr(
"alias_is_default",
alias is None if alias_is_default is None else alias_is_default,
)
def __setattr__(self, name, value):
raise FrozenInstanceError
@classmethod
def from_counting_attr(
cls, name: str, ca: _CountingAttr, kw_only: bool, type=None
):
# The 'kw_only' argument is the class-level setting, and is used if the
# attribute itself does not explicitly set 'kw_only'.
# type holds the annotated value. deal with conflicts:
if type is None:
type = ca.type
elif ca.type is not None:
msg = f"Type annotation and type argument cannot both be present for '{name}'."
raise ValueError(msg)
return cls(
name,
ca._default,
ca._validator,
ca.repr,
None,
ca.hash,
ca.init,
False,
ca.metadata,
type,
ca._converter,
kw_only if ca.kw_only is None else ca.kw_only,
ca.eq,
ca.eq_key,
ca.order,
ca.order_key,
ca.on_setattr,
ca.alias,
ca.alias is None,
)
# Don't use attrs.evolve since fields(Attribute) doesn't work
def evolve(self, **changes):
"""
Copy *self* and apply *changes*.
This works similarly to `attrs.evolve` but that function does not work
with :class:`attrs.Attribute`.
It is mainly meant to be used for `transform-fields`.
.. versionadded:: 20.3.0
"""
import copy
new = copy.copy(self)
new._setattrs(changes.items())
if "alias" in changes and "alias_is_default" not in changes:
# Explicit alias provided -- no longer the default.
_OBJ_SETATTR.__get__(new)("alias_is_default", False)
elif (
"name" in changes
and "alias" not in changes
# Don't auto-generate alias if the user picked picked the old one.
and self.alias_is_default
):
# Name changed, alias was auto-generated -- update it.
_OBJ_SETATTR.__get__(new)(
"alias", _default_init_alias_for(new.name)
)
return new
# Don't use _add_pickle since fields(Attribute) doesn't work
def __getstate__(self):
"""
Play nice with pickle.
"""
return tuple(
getattr(self, name) if name != "metadata" else dict(self.metadata)
for name in self.__slots__
)
def __setstate__(self, state):
"""
Play nice with pickle.
"""
if len(state) < len(self.__slots__):
# Pre-26.1.0 pickle without alias_is_default -- infer it
# heuristically.
state_dict = dict(zip(self.__slots__, state, strict=False))
alias_is_default = state_dict.get(
"alias"
) is None or state_dict.get("alias") == _default_init_alias_for(
state_dict["name"]
)
state = (*state, alias_is_default)
self._setattrs(zip(self.__slots__, state, strict=True))
def _setattrs(self, name_values_pairs):
bound_setattr = _OBJ_SETATTR.__get__(self)
for name, value in name_values_pairs:
if name != "metadata":
bound_setattr(name, value)
else:
bound_setattr(
name,
(
types.MappingProxyType(dict(value))
if value
else _EMPTY_METADATA_SINGLETON
),
)