cpython/Lib/dataclasses.py at 3.15 · python/cpython · GitHub

Repository navigation

History

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

368

369

370

371

372

373

374

375

376

377

378

379

380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

451

452

453

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

486

487

488

489

490

491

492

493

494

495

496

497

498

499

500

501

502

503

504

505

506

507

508

509

510

511

512

513

514

515

516

517

518

519

520

521

522

523

524

525

526

527

528

529

530

531

532

533

534

535

536

537

538

539

540

541

542

543

544

545

546

547

548

549

550

551

552

553

554

555

556

557

558

559

560

561

562

563

564

565

566

567

568

569

570

571

572

573

574

575

576

577

578

579

580

581

582

583

584

585

586

587

588

589

590

591

592

593

594

595

596

597

598

599

600

601

602

603

604

605

606

607

608

609

610

611

612

613

614

615

616

617

618

619

620

621

622

623

624

625

626

627

628

629

630

631

632

633

634

635

636

637

638

639

640

641

642

643

644

645

646

647

648

649

650

651

652

653

654

655

656

657

658

659

660

661

662

663

664

665

666

667

668

669

670

671

672

673

674

675

676

677

678

679

680

681

682

683

684

685

686

687

688

689

690

691

692

693

694

695

696

697

698

699

700

701

702

703

704

705

706

707

708

709

710

711

712

713

714

715

716

717

718

719

720

721

722

723

724

725

726

727

728

729

730

731

732

733

734

735

736

737

738

739

740

741

742

743

744

745

746

747

748

749

750

751

752

753

754

755

756

757

758

759

760

761

762

763

764

765

766

767

768

769

770

771

772

773

774

775

776

777

778

779

780

781

782

783

784

785

786

787

788

789

790

791

792

793

794

795

796

797

798

799

800

801

802

803

804

805

806

807

808

809

810

811

812

813

814

815

816

817

818

819

820

821

822

823

824

825

826

827

828

829

830

831

832

833

834

835

836

837

838

839

840

841

842

843

844

845

846

847

848

849

850

851

852

853

854

855

856

857

858

859

860

861

862

863

864

865

866

867

868

869

870

871

872

873

874

875

876

877

878

879

880

881

882

883

884

885

886

887

888

889

890

891

892

893

894

895

896

897

898

899

900

901

902

903

904

905

906

907

908

909

910

911

912

913

914

915

916

917

918

919

920

921

922

923

924

925

926

927

928

929

930

931

932

933

934

935

936

937

938

939

940

941

942

943

944

945

946

947

948

949

950

951

952

953

954

955

956

957

958

959

960

961

962

963

964

965

966

967

968

969

970

971

972

973

974

975

976

977

978

979

980

981

982

983

984

985

986

987

988

989

990

991

992

993

994

995

996

997

998

999

1000

import sys

import types

import keyword

import itertools

import annotationlib

import abc

from reprlib import recursive_repr

lazy import copy

lazy import re

__all__ = ['dataclass',

'field',

'Field',

'FrozenInstanceError',

'InitVar',

'KW_ONLY',

'MISSING',

# Helper functions.

'fields',

'asdict',

'astuple',

'make_dataclass',

'replace',

'is_dataclass',

]

# Conditions for adding methods. The boxes indicate what action the

# dataclass decorator takes. For all of these tables, when I talk

# about init=, repr=, eq=, order=, unsafe_hash=, or frozen=, I'm

# referring to the arguments to the @dataclass decorator. When

# checking if a dunder method already exists, I mean check for an

# entry in the class's __dict__. I never check to see if an attribute

# is defined in a base class.

# Key:

# +=========+=========================================+

# + Value | Meaning |

# +=========+=========================================+

# | <blank> | No action: no method is added. |

# +---------+-----------------------------------------+

# | add | Generated method is added. |

# +---------+-----------------------------------------+

# | raise | TypeError is raised. |

# +---------+-----------------------------------------+

# | None | Attribute is set to None. |

# +=========+=========================================+

# __init__

# +--- init= parameter

# |

# v | | |

# | no | yes | <--- class has __init__ in __dict__?

# +=======+=======+=======+

# | False | | |

# +-------+-------+-------+

# | True | add | | <- the default

# +=======+=======+=======+

# __repr__

# +--- repr= parameter

# |

# v | | |

# | no | yes | <--- class has __repr__ in __dict__?

# +=======+=======+=======+

# | False | | |

# +-------+-------+-------+

# | True | add | | <- the default

# +=======+=======+=======+

# __setattr__

# __delattr__

# +--- frozen= parameter

# |

# v | | |

# | no | yes | <--- class has __setattr__ or __delattr__ in __dict__?

# +=======+=======+=======+

# | False | | | <- the default

# +-------+-------+-------+

# | True | add | raise |

# +=======+=======+=======+

# Raise because not adding these methods would break the "frozen-ness"

# of the class.

# __eq__

# +--- eq= parameter

# |

# v | | |

# | no | yes | <--- class has __eq__ in __dict__?

# +=======+=======+=======+

# | False | | |

# +-------+-------+-------+

# | True | add | | <- the default

# +=======+=======+=======+

# __lt__

# __le__

# __gt__

# __ge__

# +--- order= parameter

# |

# v | | |

# | no | yes | <--- class has any comparison method in __dict__?

# +=======+=======+=======+

# | False | | | <- the default

# +-------+-------+-------+

# | True | add | raise |

# +=======+=======+=======+

# Raise because to allow this case would interfere with using

# functools.total_ordering.

# __hash__

# +------------------- unsafe_hash= parameter

# | +----------- eq= parameter

# | | +--- frozen= parameter

# | | |

# v v v | | |

# | no | yes | <--- class has explicitly defined __hash__

# +=======+=======+=======+========+========+

# +-------+-------+-------+--------+--------+

# +-------+-------+-------+--------+--------+

# +-------+-------+-------+--------+--------+

# +-------+-------+-------+--------+--------+

# +-------+-------+-------+--------+--------+

# +-------+-------+-------+--------+--------+

# +-------+-------+-------+--------+--------+

# +=======+=======+=======+========+========+

# For boxes that are blank, __hash__ is untouched and therefore

# inherited from the base class. If the base is object, then

# id-based hashing is used.

# Note that a class may already have __hash__=None if it specified an

# __eq__ method in the class body (not one that was created by

# @dataclass).

# See _hash_action (below) for a coded version of this table.

# __match_args__

# +--- match_args= parameter

# |

# v | | |

# | no | yes | <--- class has __match_args__ in __dict__?

# +=======+=======+=======+

# | False | | |

# +-------+-------+-------+

# | True | add | | <- the default

# +=======+=======+=======+

# __match_args__ is always added unless the class already defines it. It is a

# tuple of __init__ parameter names; non-init fields must be matched by keyword.

# Raised when an attempt is made to modify a frozen class.

class FrozenInstanceError(AttributeError): pass

# A sentinel object for default values to signal that a default

# factory will be used. This is given a nice repr() which will appear

# in the function signature of dataclasses' constructors.

class _HAS_DEFAULT_FACTORY_CLASS:

def __repr__(self):

return '<factory>'

_HAS_DEFAULT_FACTORY = _HAS_DEFAULT_FACTORY_CLASS()

# A sentinel object to detect if a parameter is supplied or not.

MISSING = sentinel("MISSING")

# A sentinel object to indicate that following fields are keyword-only by

# default.

KW_ONLY = sentinel("KW_ONLY")

# Since most per-field metadata will be unused, create an empty

# read-only dictionary that can be shared among all fields.

_EMPTY_METADATA = frozendict()

# Markers for the various kinds of fields and pseudo-fields.

class _FIELD_BASE:

def __init__(self, name):

self.name = name

def __repr__(self):

return self.name

_FIELD = _FIELD_BASE('_FIELD')

_FIELD_CLASSVAR = _FIELD_BASE('_FIELD_CLASSVAR')

_FIELD_INITVAR = _FIELD_BASE('_FIELD_INITVAR')

# The name of an attribute on the class where we store the Field

# objects. Also used to check if a class is a Data Class.

_FIELDS = '__dataclass_fields__'

# The name of an attribute on the class that stores the parameters to

# @dataclass.

_PARAMS = '__dataclass_params__'

# The name of the function, that if it exists, is called at the end of

# __init__.

_POST_INIT_NAME = '__post_init__'

# String regex that string annotations for ClassVar or InitVar must match.

# This regular expression is compiled on demand so that 're' module can be imported lazily

_MODULE_IDENTIFIER_RE = None

# Atomic immutable types which don't require any recursive handling and for which deepcopy

# returns the same object. We can provide a fast-path for these types in asdict and astuple.

_ATOMIC_TYPES = frozenset({

# Common JSON Serializable types

types.NoneType,

bool,

int,

float,

str,

# Other common types

complex,

bytes,

# Other types that are also unaffected by deepcopy

types.EllipsisType,

types.NotImplementedType,

types.CodeType,

types.BuiltinFunctionType,

types.FunctionType,

type,

range,

property,

})

# Any marker is used in `make_dataclass` to mark unannotated fields as `Any`

# without importing `typing` module.

_ANY_MARKER = object()

class InitVar:

__slots__ = ('type', )

def __init__(self, type):

self.type = type

def __repr__(self):

if isinstance(self.type, type):

type_name = self.type.__name__

else:

# typing objects, e.g. List[int]

type_name = repr(self.type)

return f'dataclasses.InitVar[{type_name}]'

def __class_getitem__(cls, type):

return InitVar(type)

# Instances of Field are only ever created from within this module,

# and only from the field() function, although Field instances are

# exposed externally as (conceptually) read-only objects.

# name and type are filled in after the fact, not in __init__.

# They're not known at the time this class is instantiated, but it's

# convenient if they're available later.

# When cls._FIELDS is filled in with a list of Field objects, the name

# and type fields will have been populated.

class Field:

__slots__ = ('name',

'type',

'default',

'default_factory',

'repr',

'hash',

'init',

'compare',

'metadata',

'kw_only',

'doc',

'_field_type', # Private: not to be used by user code.

)

def __init__(self, default, default_factory, init, repr, hash, compare,

metadata, kw_only, doc):

self.name = None

self.type = None

self.default = default

self.default_factory = default_factory

self.init = init

self.repr = repr

self.hash = hash

self.compare = compare

self.metadata = (_EMPTY_METADATA

if metadata is None else

types.MappingProxyType(metadata))

self.kw_only = kw_only

self.doc = doc

self._field_type = None

@recursive_repr()

def __repr__(self):

return ('Field('

f'name={self.name!r},'

f'type={self.type!r},'

f'default={self.default!r},'

f'default_factory={self.default_factory!r},'

f'init={self.init!r},'

f'repr={self.repr!r},'

f'hash={self.hash!r},'

f'compare={self.compare!r},'

f'metadata={self.metadata!r},'

f'kw_only={self.kw_only!r},'

f'doc={self.doc!r},'

f'_field_type={self._field_type}'

')')

# This is used to support the PEP 487 __set_name__ protocol in the

# case where we're using a field that contains a descriptor as a

# default value. For details on __set_name__, see

# https://peps.python.org/pep-0487/#implementation-details.

# Note that in _process_class, this Field object is overwritten

# with the default value, so the end result is a descriptor that

# had __set_name__ called on it at the right time.

def __set_name__(self, owner, name):

func = getattr(type(self.default), '__set_name__', None)

if func:

# There is a __set_name__ method on the descriptor, call

# it.

func(self.default, owner, name)

__class_getitem__ = classmethod(types.GenericAlias)

class _DataclassParams:

__slots__ = ('init',

'repr',

'eq',

'order',

'unsafe_hash',

'frozen',

'match_args',

'kw_only',

'slots',

'weakref_slot',

)

def __init__(self,

init, repr, eq, order, unsafe_hash, frozen,

match_args, kw_only, slots, weakref_slot):

self.init = init

self.repr = repr

self.eq = eq

self.order = order

self.unsafe_hash = unsafe_hash

self.frozen = frozen

self.match_args = match_args

self.kw_only = kw_only

self.slots = slots

self.weakref_slot = weakref_slot

def __repr__(self):

return ('_DataclassParams('

f'init={self.init!r},'

f'repr={self.repr!r},'

f'eq={self.eq!r},'

f'order={self.order!r},'

f'unsafe_hash={self.unsafe_hash!r},'

f'frozen={self.frozen!r},'

f'match_args={self.match_args!r},'

f'kw_only={self.kw_only!r},'

f'slots={self.slots!r},'

f'weakref_slot={self.weakref_slot!r}'

')')

# This function is used instead of exposing Field creation directly,

# so that a type checker can be told (via overloads) that this is a

# function whose type depends on its parameters.

def field(*, default=MISSING, default_factory=MISSING, init=True, repr=True,

hash=None, compare=True, metadata=None, kw_only=MISSING, doc=None):

"""Return an object to identify dataclass fields.

default is the default value of the field. default_factory is a

0-argument function called to initialize a field's value. If init

is true, the field will be a parameter to the class's __init__()

function. If repr is true, the field will be included in the

object's repr(). If hash is true, the field will be included in the

object's hash(). If compare is true, the field will be used in

comparison functions. metadata, if specified, must be a mapping

which is stored but not otherwise examined by dataclass. If kw_only

is true, the field will become a keyword-only parameter to

__init__(). doc is an optional docstring for this field.

It is an error to specify both default and default_factory.

"""

if default is not MISSING and default_factory is not MISSING:

raise ValueError('cannot specify both default and default_factory')

return Field(default, default_factory, init, repr, hash, compare,

metadata, kw_only, doc)

def _fields_in_init_order(fields):

# Returns the fields as __init__ will output them. It returns 2 tuples:

# the first for normal args, and the second for keyword args.

return (tuple(f for f in fields if f.init and not f.kw_only),

tuple(f for f in fields if f.init and f.kw_only)

)

def _tuple_str(obj_name, fields):

# Return a string representing each field of obj_name as a tuple

# member. So, if fields is ['x', 'y'] and obj_name is "self",

# return "(self.x,self.y)".

# Special case for the 0-tuple.

if not fields:

return '()'

# Note the trailing comma, needed if this turns out to be a 1-tuple.

return f'({",".join([f"{obj_name}.{f.name}" for f in fields])},)'

class _FuncBuilder:

def __init__(self, globals):

self.names = []

self.src = []

self.globals = globals

self.locals = {}

self.overwrite_errors = {}

self.unconditional_adds = {}

self.method_annotations = {}

def add_fn(self, name, args, body, *, locals=None, return_type=MISSING,

overwrite_error=False, unconditional_add=False, decorator=None,

annotation_fields=None):

if locals is not None:

self.locals.update(locals)

# Keep track if this method is allowed to be overwritten if it already

# exists in the class. The error is method-specific, so keep it with

# the name. We'll use this when we generate all of the functions in

# the add_fns_to_class call. overwrite_error is either True, in which

# case we'll raise an error, or it's a string, in which case we'll

# raise an error and append this string.

if overwrite_error:

self.overwrite_errors[name] = overwrite_error

# Should this function always overwrite anything that's already in the

# class? The default is to not overwrite a function that already

# exists.

if unconditional_add:

self.unconditional_adds[name] = True

self.names.append(name)

if annotation_fields is not None:

self.method_annotations[name] = (annotation_fields, return_type)

args = ','.join(args)

body = '\n'.join(body)

# Compute the text of the entire function, add it to the text we're generating.

self.src.append(f'{f' {decorator}\n' if decorator else ''} def {name}({args}):\n{body}')

def add_fns_to_class(self, cls):

# The source to all of the functions we're generating.

fns_src = '\n'.join(self.src)

# The locals they use.

local_vars = ','.join(self.locals.keys())

# The names of all of the functions, used for the return value of the

# outer function. Need to handle the 0-tuple specially.

if len(self.names) == 0:

return_names = '()'

else:

return_names =f'({",".join(self.names)},)'

# txt is the entire function we're going to execute, including the

# bodies of the functions we're defining. Here's a greatly simplified

# version:

# def __create_fn__():

# def __init__(self, x, y):

# self.x = x

# self.y = y

# @recursive_repr

# def __repr__(self):

# return f"cls(x={self.x!r},y={self.y!r})"

# return __init__,__repr__

txt = f"def __create_fn__({local_vars}):\n{fns_src}\n return {return_names}"

ns = {}

exec(txt, self.globals, ns)

fns = ns['__create_fn__'](**self.locals)

# Now that we've generated the functions, assign them into cls.

for name, fn in zip(self.names, fns):

fn.__qualname__ = f"{cls.__qualname__}.{fn.__name__}"

try:

annotation_fields, return_type = self.method_annotations[name]

except KeyError:

pass

else:

annotate_fn = _make_annotate_function(cls, name, annotation_fields, return_type)

fn.__annotate__ = annotate_fn

if self.unconditional_adds.get(name, False):

setattr(cls, name, fn)

else:

already_exists = _set_new_attribute(cls, name, fn)

# See if it's an error to overwrite this particular function.

if already_exists and (msg_extra := self.overwrite_errors.get(name)):

error_msg = (f'Cannot overwrite attribute {fn.__name__} '

f'in class {cls.__name__}')

if not msg_extra is True:

error_msg = f'{error_msg} {msg_extra}'

raise TypeError(error_msg)

def _make_annotate_function(__class__, method_name, annotation_fields, return_type):

# Create an __annotate__ function for a dataclass

# Try to return annotations in the same format as they would be

# from a regular __init__ function

def __annotate__(format, /):

Format = annotationlib.Format

match format:

case Format.VALUE | Format.FORWARDREF | Format.STRING:

cls_annotations = {}

for base in reversed(__class__.__mro__):

cls_annotations.update(

annotationlib.get_annotations(base, format=format)

)

new_annotations = {}

for k in annotation_fields:

# gh-142214: The annotation may be missing in unusual dynamic cases.

# If so, just skip it.

try:

new_annotations[k] = cls_annotations[k]

except KeyError:

pass

if return_type is not MISSING:

if format == Format.STRING:

new_annotations["return"] = annotationlib.type_repr(return_type)

else:

new_annotations["return"] = return_type

return new_annotations

case _:

raise NotImplementedError(format)

# This is a flag for _add_slots to know it needs to regenerate this method

# In order to remove references to the original class when it is replaced

__annotate__.__generated_by_dataclasses__ = True

__annotate__.__qualname__ = f"{__class__.__qualname__}.{method_name}.__annotate__"

return __annotate__

def _field_assign(frozen, name, value, self_name):

# If we're a frozen class, then assign to our fields in __init__

# via object.__setattr__. Otherwise, just use a simple

# assignment.

# self_name is what "self" is called in this function: don't

# hard-code "self", since that might be a field name.

if frozen:

return f' __dataclass_builtins_object__.__setattr__({self_name},{name!r},{value})'

return f' {self_name}.{name}={value}'

def _field_init(f, frozen, globals, self_name, slots):

# Return the text of the line in the body of __init__ that will

# initialize this field.

default_name = f'__dataclass_dflt_{f.name}__'

if f.default_factory is not MISSING:

if f.init:

# This field has a default factory. If a parameter is

# given, use it. If not, call the factory.

globals[default_name] = f.default_factory

value = (f'{default_name}() '

f'if {f.name} is __dataclass_HAS_DEFAULT_FACTORY__ '

f'else {f.name}')

else:

# This is a field that's not in the __init__ params, but

# has a default factory function. It needs to be

# initialized here by calling the factory function,

# because there's no other way to initialize it.

# For a field initialized with a default=defaultvalue, the

# class dict just has the default value

# (cls.fieldname=defaultvalue). But that won't work for a

# default factory, the factory must be called in __init__

# and we must assign that to self.fieldname. We can't

# fall back to the class dict's value, both because it's

# not set, and because it might be different per-class

# (which, after all, is why we have a factory function!).

globals[default_name] = f.default_factory

value = f'{default_name}()'

else:

# No default factory.

if f.init:

if f.default is MISSING:

# There's no default, just do an assignment.

value = f.name

elif f.default is not MISSING:

globals[default_name] = f.default

value = f.name

else:

# If the class has slots, then initialize this field.

if slots and f.default is not MISSING:

globals[default_name] = f.default

value = default_name

else:

# This field does not need initialization: reading from it will

# just use the class attribute that contains the default.

# Signify that to the caller by returning None.

return None

# Only test this now, so that we can create variables for the

# default. However, return None to signify that we're not going

# to actually do the assignment statement for InitVars.

if f._field_type is _FIELD_INITVAR:

return None

# Now, actually generate the field assignment.

return _field_assign(frozen, f.name, value, self_name)

def _init_param(f):

# Return the __init__ parameter string for this field. For

# example, the equivalent of 'x:int=3' (except instead of 'int',

# reference a variable set to int, and instead of '3', reference a

# variable set to 3).

if f.default is MISSING and f.default_factory is MISSING:

# There's no default, and no default_factory, just output the

# variable name and type.

default = ''

elif f.default is not MISSING:

# There's a default, this will be the name that's used to look

# it up.

default = f'=__dataclass_dflt_{f.name}__'

elif f.default_factory is not MISSING:

# There's a factory function. Set a marker.

default = '=__dataclass_HAS_DEFAULT_FACTORY__'

return f'{f.name}{default}'

def _init_fn(fields, std_fields, kw_only_fields, frozen, has_post_init,

self_name, func_builder, slots):

# fields contains both real fields and InitVar pseudo-fields.

# Make sure we don't have fields without defaults following fields

# with defaults. This actually would be caught when exec-ing the

# function source code, but catching it here gives a better error

# message, and future-proofs us in case we build up the function

# using ast.

seen_default = None

for f in std_fields:

# Only consider the non-kw-only fields in the __init__ call.

if f.init:

if not (f.default is MISSING and f.default_factory is MISSING):

seen_default = f

elif seen_default:

raise TypeError(f'non-default argument {f.name!r} '

f'follows default argument {seen_default.name!r}')

annotation_fields = [f.name for f in fields if f.init]

locals = {'__dataclass_HAS_DEFAULT_FACTORY__': _HAS_DEFAULT_FACTORY,

'__dataclass_builtins_object__': object}

body_lines = []

for f in fields:

line = _field_init(f, frozen, locals, self_name, slots)

# line is None means that this field doesn't require

# initialization (it's a pseudo-field). Just skip it.

if line:

body_lines.append(line)

# Does this class have a post-init function?

if has_post_init:

params_str = ','.join(f.name for f in fields

if f._field_type is _FIELD_INITVAR)

body_lines.append(f' {self_name}.{_POST_INIT_NAME}({params_str})')

# If no body lines, use 'pass'.

if not body_lines:

body_lines = [' pass']

_init_params = [_init_param(f) for f in std_fields]

if kw_only_fields:

# Add the keyword-only args. Because the * can only be added if

# there's at least one keyword-only arg, there needs to be a test here

# (instead of just concatenating the lists together).

_init_params += ['*']

_init_params += [_init_param(f) for f in kw_only_fields]

func_builder.add_fn('__init__',

[self_name] + _init_params,

body_lines,

locals=locals,

return_type=None,

annotation_fields=annotation_fields)

def _frozen_set_del_attr(cls, fields, func_builder):

locals = {'__class__': cls,

'FrozenInstanceError': FrozenInstanceError}

condition = 'type(self) is __class__'

if fields:

condition += ' or name in {' + ', '.join(repr(f.name) for f in fields) + '}'

func_builder.add_fn('__setattr__',

('self', 'name', 'value'),

(f' if {condition}:',

' raise FrozenInstanceError(f"cannot assign to field {name!r}")',

f' super(__class__, self).__setattr__(name, value)'),

locals=locals,

overwrite_error=True)

func_builder.add_fn('__delattr__',

('self', 'name'),

(f' if {condition}:',

' raise FrozenInstanceError(f"cannot delete field {name!r}")',

f' super(__class__, self).__delattr__(name)'),

locals=locals,

overwrite_error=True)

def _is_classvar(a_type, typing):

return (a_type is typing.ClassVar

or (typing.get_origin(a_type) is typing.ClassVar))

def _is_initvar(a_type, dataclasses):

# The module we're checking against is the module we're

# currently in (dataclasses.py).

return (a_type is dataclasses.InitVar

or type(a_type) is dataclasses.InitVar)

def _is_kw_only(a_type, dataclasses):

return a_type is dataclasses.KW_ONLY

def _get_type_from_annotation(annotation, cls):

# Loosely parse a string annotation and return its type.

# We can't perform a full type hint evaluation at the point where @dataclass

# was invoked because class's module is not fully initialized yet. So we resort

# to parsing string annotation using regexp, and extracting a type before

# the first square bracket.

# - annotation is a string type annotation

# - cls is the class that this annotation was found in

# Since this test does not do a local namespace lookup (and

# instead only a module (global) lookup), there are some things it

# gets wrong.

# With string annotations, cv0 will be detected as a ClassVar:

# CV = ClassVar

# @dataclass

# class C0:

# cv0: CV

# But in this example cv1 will not be detected as a ClassVar:

# @dataclass

# class C1:

# CV = ClassVar

# cv1: CV

# In C1, the code in this function (_is_type) will look up "CV" in

# the module and not find it, so it will not consider cv1 as a

# ClassVar. This is a fairly obscure corner case, and the best

# way to fix it would be to eval() the string "CV" with the

# correct global and local namespaces. However that would involve

# a eval() penalty for every single field of every dataclass

# that's defined. It was judged not worth it.

# String regex that string annotations for ClassVar or InitVar must match.

# Allows "identifier.identifier[" or "identifier[".

# https://github.com/python/cpython/issues/77634 for details.

global _MODULE_IDENTIFIER_RE

if _MODULE_IDENTIFIER_RE is None:

_MODULE_IDENTIFIER_RE = re.compile(r'^\s*(\w+(?:\s*\.\s*\w+)*)')

match = _MODULE_IDENTIFIER_RE.prefixmatch(annotation)

if not match:

return None

# Note: _MODULE_IDENTIFIER_RE guarantees that path is non-empty

path = match[1].split(".")

root = sys.modules.get(cls.__module__)

for path_item in path:

try:

root = getattr(root, path_item.strip(), None)

except Exception:

# Like annotationlib, ignore lazy imports that cannot be resolved.

return None

if root is None:

return None

return root

def _get_field(cls, a_name, a_type, default_kw_only):

# Return a Field object for this field name and type. ClassVars and

# InitVars are also returned, but marked as such (see f._field_type).

# default_kw_only is the value of kw_only to use if there isn't a field()

# that defines it.

# If the default value isn't derived from Field, then it's only a

# normal default value. Convert it to a Field().

default = getattr(cls, a_name, MISSING)

if isinstance(default, Field):

f = default

else:

if isinstance(default, types.MemberDescriptorType):

# This is a field in __slots__, so it has no default value.

default = MISSING

f = field(default=default)

# Only at this point do we know the name and the type. Set them.

f.name = a_name

f.type = a_type

# Assume it's a normal field until proven otherwise. We're next

# going to decide if it's a ClassVar or InitVar, everything else

# is just a normal field.

f._field_type = _FIELD

# In addition to checking for actual types here, also check for

# string annotations. get_type_hints() won't always work for us

# (see https://github.com/python/typing/issues/508 for example),

# plus it's expensive and would require an eval for every string

# annotation. So, make a best effort to see if this is a ClassVar

# or InitVar using regex's and checking that the thing referenced

# is actually of the correct type.

# For the complete discussion, see https://bugs.python.org/issue33453

if isinstance(a_type, str):

a_type_annotation = _get_type_from_annotation(a_type, cls)

else:

a_type_annotation = a_type

# If typing has not been imported, then it's impossible for any

# annotation to be a ClassVar. So, only look for ClassVar if

# typing has been imported by any module (not necessarily cls's

# module).

typing = sys.modules.get('typing')

if typing:

if _is_classvar(a_type_annotation, typing):

f._field_type = _FIELD_CLASSVAR

# If the type is InitVar, or if it's a matching string annotation,

# then it's an InitVar.

if f._field_type is _FIELD:

# The module we're checking against is the module we're

# currently in (dataclasses.py).

dataclasses = sys.modules[__name__]

if _is_initvar(a_type_annotation, dataclasses):

f._field_type = _FIELD_INITVAR

# Validations for individual fields. This is delayed until now,

# instead of in the Field() constructor, since only here do we

# know the field name, which allows for better error reporting.

# Special restrictions for ClassVar and InitVar.

if f._field_type in (_FIELD_CLASSVAR, _FIELD_INITVAR):

if f.default_factory is not MISSING:

raise TypeError(f'field {f.name} cannot have a '

'default factory')

# Should I check for other field settings? default_factory

# seems the most serious to check for. Maybe add others. For

# example, how about init=False (or really,

# init=<not-the-default-init-value>)? It makes no sense for

# ClassVar and InitVar to specify init=<anything>.

# kw_only validation and assignment.

if f._field_type in (_FIELD, _FIELD_INITVAR):

# For real and InitVar fields, if kw_only wasn't specified use the

# default value.

if f.kw_only is MISSING:

f.kw_only = default_kw_only

else:

# Make sure kw_only isn't set for ClassVars

assert f._field_type is _FIELD_CLASSVAR

if f.kw_only is not MISSING:

raise TypeError(f'field {f.name} is a ClassVar but specifies '

'kw_only')

# For real fields, disallow mutable defaults. Use unhashable as a proxy

# indicator for mutability. Read the __hash__ attribute from the class,

# not the instance.

if f._field_type is _FIELD and f.default.__class__.__hash__ is None:

raise ValueError(f'mutable default {type(f.default)} for field '

f'{f.name} is not allowed: use default_factory')

return f

def _set_new_attribute(cls, name, value):

# Never overwrites an existing attribute. Returns True if the

# attribute already exists.

if name in cls.__dict__:

return True

setattr(cls, name, value)

return False

# Decide if/how we're going to create a hash function. Key is

# (unsafe_hash, eq, frozen, does-hash-exist). Value is the action to

# take. The common case is to do nothing, so instead of providing a

# function that is a no-op, use None to signify that.

def _hash_set_none(cls, fields, func_builder):

# It's sort of a hack that I'm setting this here, instead of at

# func_builder.add_fns_to_class time, but since this is an exceptional case

# (it's not setting an attribute to a function, but to a scalar value),

# just do it directly here. I might come to regret this.

cls.__hash__ = None

def _hash_add(cls, fields, func_builder):

flds = [f for f in fields if (f.compare if f.hash is None else f.hash)]

self_tuple = _tuple_str('self', flds)

func_builder.add_fn('__hash__',

('self',),

[f' return hash({self_tuple})'],

unconditional_add=True)

def _hash_exception(cls, fields, func_builder):

# Raise an exception.

raise TypeError(f'Cannot overwrite attribute __hash__ '

f'in class {cls.__name__}')

# +-------------------------------------- unsafe_hash?

# | +------------------------------- eq?

# | | +------------------------ frozen?

# | | | +---------------- has-explicit-hash?

# | | | |

# | | | | +------- action

# | | | | |

# v v v v v

_hash_action = {(False, False, False, False): None,

(False, False, False, True ): None,

(False, False, True, False): None,

(False, False, True, True ): None,

(False, True, False, False): _hash_set_none,

(False, True, False, True ): None,

(False, True, True, False): _hash_add,

(False, True, True, True ): None,

(True, False, False, False): _hash_add,

(True, False, False, True ): _hash_exception,

(True, False, True, False): _hash_add,

(True, False, True, True ): _hash_exception,

(True, True, False, False): _hash_add,

(True, True, False, True ): _hash_exception,

(True, True, True, False): _hash_add,

(True, True, True, True ): _hash_exception,

}

# See https://bugs.python.org/issue32929#msg312829 for an if-statement

# version of this table.

# A non-data descriptor to autogenerate class docstring

# from the signature of its __init__ method on demand.

# The primary reason is to be able to lazy import `inspect` module.

class _AutoDocstring:

def __get__(self, _obj, cls):

try:

# In some cases fetching a signature is not possible.

# But, we surely should not fail in this case.

import inspect

text_sig = str(inspect.signature(

cls,

annotation_format=annotationlib.Format.FORWARDREF,

)).replace(' -> None', '')

except TypeError, ValueError:

text_sig = ''

doc = cls.__name__ + text_sig

setattr(cls, '__doc__', doc)

return doc

_auto_docstring = _AutoDocstring()

View remainder of file in raw view

cpython/Lib/dataclasses.py at 3.15 · python/cpython · GitHub

Repository navigation

Expand file tree

Breadcrumbs

dataclasses.py

Latest commit

History

Breadcrumbs

dataclasses.py

File metadata and controls