| import sys |
| import types |
| from copy import deepcopy |
| import inspect |
| |
| __all__ = ['dataclass', |
| 'field', |
| 'FrozenInstanceError', |
| 'InitVar', |
| 'MISSING', |
| |
| # Helper functions. |
| 'fields', |
| 'asdict', |
| 'astuple', |
| 'make_dataclass', |
| 'replace', |
| 'is_dataclass', |
| ] |
| |
| # 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() |
| |
| # 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. |
| _FIELD = object() # An actual field. |
| _FIELD_CLASSVAR = object() # Not a field, but a ClassVar. |
| _FIELD_INITVAR = object() # Not a field, but an 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. |
| _MARKER = '__dataclass_fields__' |
| |
| # The name of the function, that if it exists, is called at the end of |
| # __init__. |
| _POST_INIT_NAME = '__post_init__' |
| |
| |
| class _InitVarMeta(type): |
| def __getitem__(self, params): |
| return self |
| |
| class InitVar(metaclass=_InitVarMeta): |
| pass |
| |
| |
| # 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._MARKER 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', |
| '_field_type', # Private: not to be used by user code. |
| ) |
| |
| def __init__(self, default, default_factory, init, repr, hash, compare, |
| metadata): |
| 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 or len(metadata) == 0 else |
| types.MappingProxyType(metadata)) |
| self._field_type = None |
| |
| def __repr__(self): |
| return ('Field(' |
| f'name={self.name!r},' |
| f'type={self.type},' |
| f'default={self.default},' |
| f'default_factory={self.default_factory},' |
| f'init={self.init},' |
| f'repr={self.repr},' |
| f'hash={self.hash},' |
| f'compare={self.compare},' |
| f'metadata={self.metadata}' |
| ')') |
| |
| |
| # 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): |
| """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. |
| |
| 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) |
| |
| |
| 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 len(fields) == 0: |
| 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])},)' |
| |
| |
| def _create_fn(name, args, body, globals=None, locals=None, |
| return_type=MISSING): |
| # Note that we mutate locals when exec() is called. Caller beware! |
| if locals is None: |
| locals = {} |
| return_annotation = '' |
| if return_type is not MISSING: |
| locals['_return_type'] = return_type |
| return_annotation = '->_return_type' |
| args = ','.join(args) |
| body = '\n'.join(f' {b}' for b in body) |
| |
| txt = f'def {name}({args}){return_annotation}:\n{body}' |
| |
| exec(txt, globals, locals) |
| return locals[name] |
| |
| |
| 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'object.__setattr__({self_name},{name!r},{value})' |
| return f'{self_name}.{name}={value}' |
| |
| |
| def _field_init(f, frozen, globals, self_name): |
| # Return the text of the line in the body of __init__ that will |
| # initialize this field. |
| |
| default_name = f'_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 _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: |
| # This field does not need initialization. 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 == _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'=_dflt_{f.name}' |
| elif f.default_factory is not MISSING: |
| # There's a factory function. Set a marker. |
| default = '=_HAS_DEFAULT_FACTORY' |
| return f'{f.name}:_type_{f.name}{default}' |
| |
| |
| def _init_fn(fields, frozen, has_post_init, self_name): |
| # 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 = False |
| for f in fields: |
| # Only consider fields in the __init__ call. |
| if f.init: |
| if not (f.default is MISSING and f.default_factory is MISSING): |
| seen_default = True |
| elif seen_default: |
| raise TypeError(f'non-default argument {f.name!r} ' |
| 'follows default argument') |
| |
| globals = {'MISSING': MISSING, |
| '_HAS_DEFAULT_FACTORY': _HAS_DEFAULT_FACTORY} |
| |
| body_lines = [] |
| for f in fields: |
| # Do not initialize the pseudo-fields, only the real ones. |
| line = _field_init(f, frozen, globals, self_name) |
| if line is not None: |
| # line is None means that this field doesn't require |
| # initialization. Just skip it. |
| 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 += [f'{self_name}.{_POST_INIT_NAME}({params_str})'] |
| |
| # If no body lines, use 'pass'. |
| if len(body_lines) == 0: |
| body_lines = ['pass'] |
| |
| locals = {f'_type_{f.name}': f.type for f in fields} |
| return _create_fn('__init__', |
| [self_name] +[_init_param(f) for f in fields if f.init], |
| body_lines, |
| locals=locals, |
| globals=globals, |
| return_type=None) |
| |
| |
| def _repr_fn(fields): |
| return _create_fn('__repr__', |
| ['self'], |
| ['return self.__class__.__qualname__ + f"(' + |
| ', '.join([f"{f.name}={{self.{f.name}!r}}" |
| for f in fields]) + |
| ')"']) |
| |
| |
| def _frozen_setattr(self, name, value): |
| raise FrozenInstanceError(f'cannot assign to field {name!r}') |
| |
| |
| def _frozen_delattr(self, name): |
| raise FrozenInstanceError(f'cannot delete field {name!r}') |
| |
| |
| def _cmp_fn(name, op, self_tuple, other_tuple): |
| # Create a comparison function. If the fields in the object are |
| # named 'x' and 'y', then self_tuple is the string |
| # '(self.x,self.y)' and other_tuple is the string |
| # '(other.x,other.y)'. |
| |
| return _create_fn(name, |
| ['self', 'other'], |
| [ 'if other.__class__ is self.__class__:', |
| f' return {self_tuple}{op}{other_tuple}', |
| 'return NotImplemented']) |
| |
| |
| def _set_eq_fns(cls, fields): |
| # Create and set the equality comparison methods on cls. |
| # Pre-compute self_tuple and other_tuple, then re-use them for |
| # each function. |
| self_tuple = _tuple_str('self', fields) |
| other_tuple = _tuple_str('other', fields) |
| for name, op in [('__eq__', '=='), |
| ('__ne__', '!='), |
| ]: |
| _set_attribute(cls, name, _cmp_fn(name, op, self_tuple, other_tuple)) |
| |
| |
| def _set_order_fns(cls, fields): |
| # Create and set the ordering methods on cls. |
| # Pre-compute self_tuple and other_tuple, then re-use them for |
| # each function. |
| self_tuple = _tuple_str('self', fields) |
| other_tuple = _tuple_str('other', fields) |
| for name, op in [('__lt__', '<'), |
| ('__le__', '<='), |
| ('__gt__', '>'), |
| ('__ge__', '>='), |
| ]: |
| _set_attribute(cls, name, _cmp_fn(name, op, self_tuple, other_tuple)) |
| |
| |
| def _hash_fn(fields): |
| self_tuple = _tuple_str('self', fields) |
| return _create_fn('__hash__', |
| ['self'], |
| [f'return hash({self_tuple})']) |
| |
| |
| def _get_field(cls, a_name, a_type): |
| # Return a Field object, for this field name and type. ClassVars |
| # and InitVars are also returned, but marked as such (see |
| # f._field_type). |
| |
| # 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: |
| f = field(default=default) |
| |
| # Assume it's a normal field until proven otherwise. |
| f._field_type = _FIELD |
| |
| # Only at this point do we know the name and the type. Set them. |
| f.name = a_name |
| f.type = 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. |
| typing = sys.modules.get('typing') |
| if typing is not None: |
| # This test uses a typing internal class, but it's the best |
| # way to test if this is a ClassVar. |
| if (type(a_type) is typing._GenericAlias and |
| a_type.__origin__ is typing.ClassVar): |
| # This field is a ClassVar, so it's not a field. |
| f._field_type = _FIELD_CLASSVAR |
| |
| if f._field_type is _FIELD: |
| # Check if this is an InitVar. |
| if a_type is InitVar: |
| # InitVars are not fields, either. |
| f._field_type = _FIELD_INITVAR |
| |
| # Validations for fields. This is delayed until now, instead of |
| # in the Field() constructor, since only here do we know the field |
| # name, which allows 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>. |
| |
| # For real fields, disallow mutable defaults for known types. |
| if f._field_type is _FIELD and isinstance(f.default, (list, dict, set)): |
| raise ValueError(f'mutable default {type(f.default)} for field ' |
| f'{f.name} is not allowed: use default_factory') |
| |
| return f |
| |
| |
| def _find_fields(cls): |
| # Return a list of Field objects, in order, for this class (and no |
| # base classes). Fields are found from __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 deal with later. |
| |
| annotations = getattr(cls, '__annotations__', {}) |
| |
| return [_get_field(cls, a_name, a_type) |
| for a_name, a_type in annotations.items()] |
| |
| |
| def _set_attribute(cls, name, value): |
| # Raise TypeError if an attribute by this name already exists. |
| if name in cls.__dict__: |
| raise TypeError(f'Cannot overwrite attribute {name} ' |
| f'in {cls.__name__}') |
| setattr(cls, name, value) |
| |
| |
| def _process_class(cls, repr, eq, order, hash, init, frozen): |
| # 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 = {} |
| |
| # 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. |
| for b in cls.__mro__[-1:0:-1]: |
| # Only process classes that have been processed by our |
| # decorator. That is, they have a _MARKER attribute. |
| base_fields = getattr(b, _MARKER, None) |
| if base_fields: |
| for f in base_fields.values(): |
| fields[f.name] = f |
| |
| # Now find fields in our class. While doing so, validate some |
| # things, and set the default values (as class attributes) |
| # where we can. |
| for f in _find_fields(cls): |
| fields[f.name] = f |
| |
| # If the class attribute (which is the default value for |
| # this field) exists and is of type 'Field', replace it |
| # with the real default. This is so that normal class |
| # introspection sees a real default value, not a Field. |
| if isinstance(getattr(cls, f.name, None), Field): |
| if f.default is MISSING: |
| # If there's no default, delete the class attribute. |
| # This happens if we specify field(repr=False), for |
| # example (that is, we specified a field object, but |
| # no default value). Also if we're using a default |
| # factory. The class attribute should not be set at |
| # all in the post-processed class. |
| delattr(cls, f.name) |
| else: |
| setattr(cls, f.name, f.default) |
| |
| # Remember all of the fields on our class (including bases). This |
| # marks this class as being a dataclass. |
| setattr(cls, _MARKER, fields) |
| |
| # We also need to check if a parent class is frozen: frozen has to |
| # be inherited down. |
| is_frozen = frozen or cls.__setattr__ is _frozen_setattr |
| |
| # If we're generating ordering methods, we must be generating |
| # the eq methods. |
| if order and not eq: |
| raise ValueError('eq must be true if order is true') |
| |
| if init: |
| # Does this class have a post-init function? |
| has_post_init = hasattr(cls, _POST_INIT_NAME) |
| |
| # Include InitVars and regular fields (so, not ClassVars). |
| _set_attribute(cls, '__init__', |
| _init_fn(list(filter(lambda f: f._field_type |
| in (_FIELD, _FIELD_INITVAR), |
| fields.values())), |
| is_frozen, |
| has_post_init, |
| # The name to use for the "self" param |
| # in __init__. Use "self" if possible. |
| '__dataclass_self__' if 'self' in fields |
| else 'self', |
| )) |
| |
| # Get the fields as a list, and include only real fields. This is |
| # used in all of the following methods. |
| field_list = list(filter(lambda f: f._field_type is _FIELD, |
| fields.values())) |
| |
| if repr: |
| _set_attribute(cls, '__repr__', |
| _repr_fn(list(filter(lambda f: f.repr, field_list)))) |
| |
| if is_frozen: |
| _set_attribute(cls, '__setattr__', _frozen_setattr) |
| _set_attribute(cls, '__delattr__', _frozen_delattr) |
| |
| generate_hash = False |
| if hash is None: |
| if eq and frozen: |
| # Generate a hash function. |
| generate_hash = True |
| elif eq and not frozen: |
| # Not hashable. |
| _set_attribute(cls, '__hash__', None) |
| elif not eq: |
| # Otherwise, use the base class definition of hash(). That is, |
| # don't set anything on this class. |
| pass |
| else: |
| assert "can't get here" |
| else: |
| generate_hash = hash |
| if generate_hash: |
| _set_attribute(cls, '__hash__', |
| _hash_fn(list(filter(lambda f: f.compare |
| if f.hash is None |
| else f.hash, |
| field_list)))) |
| |
| if eq: |
| # Create and __eq__ and __ne__ methods. |
| _set_eq_fns(cls, list(filter(lambda f: f.compare, field_list))) |
| |
| if order: |
| # Create and __lt__, __le__, __gt__, and __ge__ methods. |
| # Create and set the comparison functions. |
| _set_order_fns(cls, list(filter(lambda f: f.compare, field_list))) |
| |
| if not getattr(cls, '__doc__'): |
| # Create a class doc-string. |
| cls.__doc__ = (cls.__name__ + |
| str(inspect.signature(cls)).replace(' -> None', '')) |
| |
| return cls |
| |
| |
| # _cls should never be specified by keyword, so start it with an |
| # underscore. The presence of _cls is used to detect if this |
| # decorator is being called with parameters or not. |
| def dataclass(_cls=None, *, init=True, repr=True, eq=True, order=False, |
| hash=None, frozen=False): |
| """Returns the same class as was passed in, with dunder methods |
| added based on the fields defined in the class. |
| |
| Examines PEP 526 __annotations__ to determine fields. |
| |
| If init is true, an __init__() method is added to the class. If |
| repr is true, a __repr__() method is added. If order is true, rich |
| comparison dunder methods are added. If hash is true, a __hash__() |
| method function is added. If frozen is true, fields may not be |
| assigned to after instance creation. |
| """ |
| |
| def wrap(cls): |
| return _process_class(cls, repr, eq, order, hash, init, frozen) |
| |
| # See if we're being called as @dataclass or @dataclass(). |
| if _cls is None: |
| # We're called with parens. |
| return wrap |
| |
| # We're called as @dataclass without parens. |
| return wrap(_cls) |
| |
| |
| def fields(class_or_instance): |
| """Return a tuple describing the fields of this dataclass. |
| |
| Accepts a dataclass or an instance of one. Tuple elements are of |
| type Field. |
| """ |
| |
| # Might it be worth caching this, per class? |
| try: |
| fields = getattr(class_or_instance, _MARKER) |
| except AttributeError: |
| raise TypeError('must be called with a dataclass type or instance') |
| |
| # Exclude pseudo-fields. Note that fields is sorted by insertion |
| # order, so the order of the tuple is as the fields were defined. |
| return tuple(f for f in fields.values() if f._field_type is _FIELD) |
| |
| |
| def _is_dataclass_instance(obj): |
| """Returns True if obj is an instance of a dataclass.""" |
| return not isinstance(obj, type) and hasattr(obj, _MARKER) |
| |
| |
| def is_dataclass(obj): |
| """Returns True if obj is a dataclass or an instance of a |
| dataclass.""" |
| return hasattr(obj, _MARKER) |
| |
| |
| def asdict(obj, *, dict_factory=dict): |
| """Return the fields of a dataclass instance as a new dictionary mapping |
| field names to field values. |
| |
| Example usage: |
| |
| @dataclass |
| class C: |
| x: int |
| y: int |
| |
| c = C(1, 2) |
| assert asdict(c) == {'x': 1, 'y': 2} |
| |
| If given, 'dict_factory' will be used instead of built-in dict. |
| The function applies recursively to field values that are |
| dataclass instances. This will also look into built-in containers: |
| tuples, lists, and dicts. |
| """ |
| if not _is_dataclass_instance(obj): |
| raise TypeError("asdict() should be called on dataclass instances") |
| return _asdict_inner(obj, dict_factory) |
| |
| def _asdict_inner(obj, dict_factory): |
| if _is_dataclass_instance(obj): |
| result = [] |
| for f in fields(obj): |
| value = _asdict_inner(getattr(obj, f.name), dict_factory) |
| result.append((f.name, value)) |
| return dict_factory(result) |
| elif isinstance(obj, (list, tuple)): |
| return type(obj)(_asdict_inner(v, dict_factory) for v in obj) |
| elif isinstance(obj, dict): |
| return type(obj)((_asdict_inner(k, dict_factory), _asdict_inner(v, dict_factory)) |
| for k, v in obj.items()) |
| else: |
| return deepcopy(obj) |
| |
| |
| def astuple(obj, *, tuple_factory=tuple): |
| """Return the fields of a dataclass instance as a new tuple of field values. |
| |
| Example usage:: |
| |
| @dataclass |
| class C: |
| x: int |
| y: int |
| |
| c = C(1, 2) |
| assert astuple(c) == (1, 2) |
| |
| If given, 'tuple_factory' will be used instead of built-in tuple. |
| The function applies recursively to field values that are |
| dataclass instances. This will also look into built-in containers: |
| tuples, lists, and dicts. |
| """ |
| |
| if not _is_dataclass_instance(obj): |
| raise TypeError("astuple() should be called on dataclass instances") |
| return _astuple_inner(obj, tuple_factory) |
| |
| def _astuple_inner(obj, tuple_factory): |
| if _is_dataclass_instance(obj): |
| result = [] |
| for f in fields(obj): |
| value = _astuple_inner(getattr(obj, f.name), tuple_factory) |
| result.append(value) |
| return tuple_factory(result) |
| elif isinstance(obj, (list, tuple)): |
| return type(obj)(_astuple_inner(v, tuple_factory) for v in obj) |
| elif isinstance(obj, dict): |
| return type(obj)((_astuple_inner(k, tuple_factory), _astuple_inner(v, tuple_factory)) |
| for k, v in obj.items()) |
| else: |
| return deepcopy(obj) |
| |
| |
| def make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True, |
| repr=True, eq=True, order=False, hash=None, frozen=False): |
| """Return a new dynamically created dataclass. |
| |
| The dataclass name will be 'cls_name'. 'fields' is an iterable |
| of either (name), (name, type) or (name, type, Field) objects. If type is |
| omitted, use the string 'typing.Any'. Field objects are created by |
| the equivalent of calling 'field(name, type [, Field-info])'. |
| |
| C = make_dataclass('C', ['x', ('y', int), ('z', int, field(init=False))], bases=(Base,)) |
| |
| is equivalent to: |
| |
| @dataclass |
| class C(Base): |
| x: 'typing.Any' |
| y: int |
| z: int = field(init=False) |
| |
| For the bases and namespace parameters, see the builtin type() function. |
| |
| The parameters init, repr, eq, order, hash, and frozen are passed to |
| dataclass(). |
| """ |
| |
| if namespace is None: |
| namespace = {} |
| else: |
| # Copy namespace since we're going to mutate it. |
| namespace = namespace.copy() |
| |
| anns = {} |
| for item in fields: |
| if isinstance(item, str): |
| name = item |
| tp = 'typing.Any' |
| elif len(item) == 2: |
| name, tp, = item |
| elif len(item) == 3: |
| name, tp, spec = item |
| namespace[name] = spec |
| anns[name] = tp |
| |
| namespace['__annotations__'] = anns |
| cls = type(cls_name, bases, namespace) |
| return dataclass(cls, init=init, repr=repr, eq=eq, order=order, |
| hash=hash, frozen=frozen) |
| |
| def replace(obj, **changes): |
| """Return a new object replacing specified fields with new values. |
| |
| This is especially useful for frozen classes. Example usage: |
| |
| @dataclass(frozen=True) |
| class C: |
| x: int |
| y: int |
| |
| c = C(1, 2) |
| c1 = replace(c, x=3) |
| assert c1.x == 3 and c1.y == 2 |
| """ |
| |
| # We're going to mutate 'changes', but that's okay because it's a new |
| # dict, even if called with 'replace(obj, **my_changes)'. |
| |
| if not _is_dataclass_instance(obj): |
| raise TypeError("replace() should be called on dataclass instances") |
| |
| # It's an error to have init=False fields in 'changes'. |
| # If a field is not in 'changes', read its value from the provided obj. |
| |
| for f in getattr(obj, _MARKER).values(): |
| if not f.init: |
| # Error if this field is specified in changes. |
| if f.name in changes: |
| raise ValueError(f'field {f.name} is declared with ' |
| 'init=False, it cannot be specified with ' |
| 'replace()') |
| continue |
| |
| if f.name not in changes: |
| changes[f.name] = getattr(obj, f.name) |
| |
| # Create the new object, which calls __init__() and __post_init__ |
| # (if defined), using all of the init fields we've added and/or |
| # left in 'changes'. |
| # If there are values supplied in changes that aren't fields, this |
| # will correctly raise a TypeError. |
| return obj.__class__(**changes) |