import re

import sys

import copy

import types

import inspect

import keyword

import itertools

import abc

from reprlib import recursive_repr

__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__

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

# | False | False | False | | | No __eq__, use the base class __hash__

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

# | False | False | True | | | No __eq__, use the base class __hash__

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

# | False | True | False | None | | <-- the default, not hashable

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

# | False | True | True | add | | Frozen, so hashable, allows override

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

# | True | False | False | add | raise | Has no __eq__, but hashable

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

# | True | False | True | add | raise | Has no __eq__, but hashable

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

# | True | True | False | add | raise | Not frozen, but hashable

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

# | True | True | True | add | raise | Frozen, so hashable

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

# 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. Use

# a class to give it a better repr.

class _MISSING_TYPE:

pass

MISSING = _MISSING_TYPE()

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

# default. Use a class to give it a better repr.

class _KW_ONLY_TYPE:

pass

KW_ONLY = _KW_ONLY_TYPE()

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

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

_EMPTY_METADATA = types.MappingProxyType({})

# 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.

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

# https://bugs.python.org/issue33453 for details.

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

# 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,

})

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',

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

)

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

metadata, kw_only):

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._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'_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):

"""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__().

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)

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 = {}

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

overwrite_error=False, unconditional_add=False, decorator=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 return_type is not MISSING:

self.locals[f'__dataclass_{name}_return_type__'] = return_type

return_annotation = f'->__dataclass_{name}_return_type__'

else:

return_annotation = ''

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}){return_annotation}:\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__}"

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 _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}:__dataclass_type_{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}')

locals = {**{f'__dataclass_type_{f.name}__': f.type for f in fields},

**{'__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 concatenting 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)

def _frozen_get_del_attr(cls, fields, func_builder):

locals = {'cls': cls,

'FrozenInstanceError': FrozenInstanceError}

condition = 'type(self) is cls'

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(cls, 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(cls, self).__delattr__(name)'),

locals=locals,

overwrite_error=True)

def _is_classvar(a_type, typing):

# This test uses a typing internal class, but it's the best way to

# test if this is a ClassVar.

return (a_type is typing.ClassVar

or (type(a_type) is typing._GenericAlias

and a_type.__origin__ 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 _is_type(annotation, cls, a_module, a_type, is_type_predicate):

# Given a type annotation string, does it refer to a_type in

# a_module? For example, when checking that annotation denotes a

# ClassVar, then a_module is typing, and a_type is

# typing.ClassVar.

# It's possible to look up a_module given a_type, but it involves

# looking in sys.modules (again!), and seems like a waste since

# the caller already knows a_module.

# - annotation is a string type annotation

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

# - a_module is the module we want to match

# - a_type is the type in that module we want to match

# - is_type_predicate is a function called with (obj, a_module)

# that determines if obj is of the desired type.

# 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.

match = _MODULE_IDENTIFIER_RE.match(annotation)

if match:

ns = None

module_name = match.group(1)

if not module_name:

# No module name, assume the class's module did

# "from dataclasses import InitVar".

ns = sys.modules.get(cls.__module__).__dict__

else:

# Look up module_name in the class's module.

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

if module and module.__dict__.get(module_name) is a_module:

ns = sys.modules.get(a_type.__module__).__dict__

if ns and is_type_predicate(ns.get(match.group(2)), a_module):

return True

return False

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 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, typing)

or (isinstance(f.type, str)

and _is_type(f.type, cls, typing, typing.ClassVar,

_is_classvar))):

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, dataclasses)

or (isinstance(f.type, str)

and _is_type(f.type, cls, dataclasses, dataclasses.InitVar,

_is_initvar))):

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.

def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen,

match_args, kw_only, slots, weakref_slot):

# Now that dicts retain insertion order, there's no reason to use

# an ordered dict. I am leveraging that ordering here, because

# derived class fields overwrite base class fields, but the order

# is defined by the base class, which is found first.

fields = {}

if cls.__module__ in sys.modules:

globals = sys.modules[cls.__module__].__dict__

else:

# Theoretically this can happen if someone writes

# a custom string to cls.__module__. In which case

# such dataclass won't be fully introspectable

# (w.r.t. typing.get_type_hints) but will still function

# correctly.

globals = {}

setattr(cls, _PARAMS, _DataclassParams(init, repr, eq, order,

unsafe_hash, frozen,

match_args, kw_only,

slots, weakref_slot))

# Find our base classes in reverse MRO order, and exclude

# ourselves. In reversed order so that more derived classes

# override earlier field definitions in base classes. As long as

# we're iterating over them, see if all or any of them are frozen.

any_frozen_base = False

# By default `all_frozen_bases` is `None` to represent a case,

# where some dataclasses does not have any bases with `_FIELDS`

all_frozen_bases = None

has_dataclass_bases = False

for b in cls.__mro__[-1:0:-1]:

# Only process classes that have been processed by our

# decorator. That is, they have a _FIELDS attribute.

base_fields = getattr(b, _FIELDS, None)

if base_fields is not None:

has_dataclass_bases = True

for f in base_fields.values():

fields[f.name] = f

if all_frozen_bases is None:

all_frozen_bases = True

current_frozen = getattr(b, _PARAMS).frozen

all_frozen_bases = all_frozen_bases and current_frozen

any_frozen_base = any_frozen_base or current_frozen

# Annotations defined specifically in this class (not in base classes).

#

# Fields are found from cls_annotations, which is guaranteed to be

# ordered. Default values are from class attributes, if a field

# has a default. If the default value is a Field(), then it

# contains additional info beyond (and possibly including) the

# actual default value. Pseudo-fields ClassVars and InitVars are

# included, despite the fact that they're not real fields. That's

# dealt with later.

cls_annotations = inspect.get_annotations(cls)

# Now find fields in our class. While doing so, validate some

# things, and set the default values (as class attributes) where

# we can.

cls_fields = []

# Get a reference to this module for the _is_kw_only() test.

KW_ONLY_seen = False

dataclasses = sys.modules[__name__]

for name, type in cls_annotations.items():

# See if this is a marker to change the value of kw_only.

if (_is_kw_only(type, dataclasses)

or (isinstance(type, str)

and _is_type(type, cls, dataclasses, dataclasses.KW_ONLY,

_is_kw_only))):

# Switch the default to kw_only=True, and ignore this

# annotation: it's not a real field.