📚 NAME
dataclasses
🚀 Quick Reference
| Use Case | Command | Description |
|---|
| Define a simple dataclass | @dataclass
class Point:
x: int
y: int | Auto-generates __init__, __repr__, __eq__ |
| Create a frozen (immutable) dataclass | @dataclass(frozen=True)
class ImmutablePoint:
x: int
y: int | Fields cannot be modified after creation |
| Use a field with a default value | @dataclass
class C:
a: int = 0
b: str = field(default="hello") | Specify default via assignment or field() |
| Use a default factory for mutable defaults | @dataclass
class D:
items: list = field(default_factory=list) | Avoids shared mutable default issue |
| Convert dataclass to dict | asdict(instance) | Recursively converts fields to dict |
| Convert dataclass to tuple | astuple(instance) | Returns field values as tuple |
| Replace fields in a frozen dataclass | replace(instance, x=new_value) | Returns new instance with specified fields changed |
| Create a dataclass dynamically | make_dataclass('C', ['x', ('y', int)]) | Returns a new dataclass class |
📖 MODULE REFERENCE
https://docs.python.org/3.10/library/dataclasses.html
The following documentation is automatically generated from the Python
source files. It may be incomplete, incorrect or include features that
are considered implementation detail and may vary between Python
implementations. When in doubt, consult the module reference at the
location listed above.
📂 CLASSES
builtins.AttributeError(builtins.Exception)
FrozenInstanceError
builtins.object
Field
InitVar
| Field(default, default_factory, init, repr, hash, compare, metadata, kw_only)
|
| # 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.
|
|
Methods defined here:
|
|
__init__(self, default, default_factory, init, repr, hash, compare, metadata, kw_only)
| Initialize self. See help(type(self)) for accurate signature.
|
|
__repr__(self)
| Return repr(self).
|
|
__set_name__(self, owner, name)
| # 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://www.python.org/dev/peps/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.
|
| ----------------------------------------------------------------------
|
Class methods defined here:
|
|
__class_getitem__ = GenericAlias(...) from builtins.type
| Represent a PEP 585 generic type
|
| E.g. for t = list[int], t.__origin__ is list and t.__args__ is (int,).
|
| ----------------------------------------------------------------------
|
Data descriptors defined here:
|
|
| - compare
| - default
| - default_factory
| - hash
| - init
| - kw_only
| - metadata
| - name
| - repr
| - type
|
| # Raised when an attempt is made to modify a frozen class.
|
|
Method resolution order:
| FrozenInstanceError
| builtins.AttributeError
| builtins.Exception
| builtins.BaseException
| builtins.object
|
|
Data descriptors defined here:
|
|
| - __weakref__ — list of weak references to the object (if defined)
|
|
| ----------------------------------------------------------------------
|
Methods inherited from builtins.AttributeError:
|
|
| - __init__(self, /, *args, **kwargs) — Initialize self.
| - __str__(self, /) — Return str(self).
|
|
| ----------------------------------------------------------------------
|
Data descriptors inherited from builtins.AttributeError:
|
|
| - name — attribute name
| - obj — object
|
|
| ----------------------------------------------------------------------
|
Static methods inherited from builtins.Exception:
|
|
| - __new__(*args, **kwargs) from builtins.type — Create and return a new object.
|
|
| ----------------------------------------------------------------------
|
Methods inherited from builtins.BaseException:
|
|
| - __delattr__(self, name, /) — Implement delattr(self, name).
| - __getattribute__(self, name, /) — Return getattr(self, name).
| - __reduce__(...) — Helper for pickle.
| - __repr__(self, /) — Return repr(self).
| - __setattr__(self, name, value, /) — Implement setattr(self, name, value).
| - __setstate__(...)
| - with_traceback(...) — Exception.with_traceback(tb) -- set self.__traceback__ to tb and return self.
|
|
| ----------------------------------------------------------------------
|
Data descriptors inherited from builtins.BaseException:
|
|
| - __cause__ — exception cause
| - __context__ — exception context
| - __dict__
| - __suppress_context__
| - __traceback__
| - args
|
| InitVar(type)
|
|
Methods defined here:
|
|
| - __init__(self, type) — Initialize self.
| - __repr__(self) — Return repr(self).
|
|
| ----------------------------------------------------------------------
|
Class methods defined here:
|
|
| - __class_getitem__(type) from builtins.type
|
|
| ----------------------------------------------------------------------
|
Data descriptors defined here:
|
|
⚙️ FUNCTIONS
🔧 asdict(obj, *, dict_factory=<class '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.
🔧 astuple(obj, *, tuple_factory=<class '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.
🔧 dataclass(cls=None, /, *, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=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 unsafe_hash is true, a
__hash__() method function is added. If frozen is true, fields may
not be assigned to after instance creation. If match_args is true,
the __match_args__ tuple is added. If kw_only is true, then by
default all fields are keyword-only. If slots is true, an
__slots__ attribute is added.
🔧 field(*, default=<dataclasses._MISSING_TYPE object at 0x7fbfaecb6bc0>, default_factory=<dataclasses._MISSING_TYPE object at 0x7fbfaecb6bc0>, init=True, repr=True, hash=None, compare=True, metadata=None, kw_only=<dataclasses._MISSING_TYPE object at 0x7fbfaecb6bc0>)
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.
🔧 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.
🔧 is_dataclass(obj)
Returns True if obj is a dataclass or an instance of a
dataclass.
🔧 make_dataclass(cls_name, fields, *, bases=(), namespace=None, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=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, unsafe_hash, and frozen are passed to
dataclass().
🔧 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
📊 DATA
KW_ONLY = <dataclasses._KW_ONLY_TYPE object>MISSING = <dataclasses._MISSING_TYPE object>__all__ = ['dataclass', 'field', 'Field', 'FrozenInstanceError', 'InitVar', ...]
📁 FILE
/usr/lib/python3.10/dataclasses.py
