Differences between revisions 2 and 6 (spanning 4 versions)

Python DataClass

dataclass is a module that supports the creation of simple classes.

Contents

Python DataClass

Decorators

@DataClass

Use the @dataclass decorator on a class to automatically generate dunder methods.

import dataclass

@dataclass.dataclass
class User:
    name: str       # 'name' has no defualt value
    id: int = 1000  # 'id' defaults to 1000

A TypeError is raised if a field without a default value follows a field with a default value.

Classes

Field

A Field object represents a field in a dataclass. For complex logic, a dataclass can be defined in terms of Field objects.

A Field object is instantiated with the field() function. This function takes the following optional named arguments:

default: default value
default_factory: callable that generates the default value as needed
init: boolean indicating that this field should be included in the generated __init__ method
repr: boolean indicating that this field should be included in the generated __repr__ method
hash: boolean indicating that this field should be included in the generated __hash__ method
compare: boolean indicating that this field should be included in the generated comparison methods (e.g. __eq__ and so on)
kw_only: boolean indicating that this field is keyword-only

A Field object has name and type atributes, as well as attribute matching the names and meanings of the field() function's arguments.

To create a dataclass with a field that defaults to an empty list, try:

import dataclass

@dataclass.dataclass
class User:
    groups: list[int] = dataclass.field(default_factory=list)

u = User()
u.groups += [1, 2, 3]

Functions

AsDict

import dataclass

@dataclass.dataclass
class Point:
     x: int
     y: int

p = Point(10, 20)
dataclass.asdict(p)  # {'x': 10, 'y': 20}

AsTuple

import dataclass

@dataclass.dataclass
class Point:
     x: int
     y: int

p = Point(10, 20)
dataclass.astuple(p)  # (10, 20)

Fields

Extract the Field objects from a dataclass.

Is_DataClass

Make_DataClass

Replace

Constants

KW_ONLY is a type annotation used for dataclasses.

import dataclass

@dataclass.dataclass
class Point:
    x: float
    _: dataclass.KW_ONLY
    y: float
    z: float

p = Point(0, y=1.5, z=2.0)

MISSING is a sentinel value used internally.

-  ⇤ ← Revision 2 as of 2023-04-11 16:44:59 → 
  Size: 1545
  Editor: DominicRicottone
  Comment:
+   ← Revision 6 as of 2023-06-15 20:44:18 → ⇥
  Size: 3104
  Editor: DominicRicottone
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
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-= Python DataClasses =
+## page was renamed from Python/DataClass
= Python DataClass =
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-'''`dataclasses`''' is a module that supports the creation of simple classes.
+'''`dataclass`''' is a module that supports the creation of simple classes.
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+Line 11:
-== Usage ==
+== Decorators ==
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-Decorate a class to generate [[Python/DunderMethod|additional methods]].
+Use the '''`@dataclass`''' decorator on a class to automatically generate [[Python/DunderMethod|dunder methods]].
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+Line 34:
-=== AsDict ===

----



=== AsTuple ===

----
+== Classes ==
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+Line 40:
-Create more complicated default behaviors for dataclass fields.
+A '''`Field`''' object represents a field in a dataclass. For complex logic, a dataclass can be defined in terms of `Field` objects.
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+Line 42:
-To create a field that defaults to an empty list, try:
+A `Field` object is instantiated with the `field()` function. This function takes the following optional named arguments:

 * `default`: default value
 * `default_factory`: callable that generates the default value as needed
 * `init`: boolean indicating that this field should be included in the generated [[Python/DunderMethod#__Init__|__init__]] method
 * `repr`: boolean indicating that this field should be included in the generated [[Python/DunderMethod#__Repr__|__repr__]] method
 * `hash`: boolean indicating that this field should be included in the generated [[Python/DunderMethod#__Hash__|__hash__]] method
 * `compare`: boolean indicating that this field should be included in the generated comparison methods (e.g. [[Python/DunderMethod#__Eq__|__eq__]] and so on)
 * `kw_only`: boolean indicating that this field is keyword-only

A `Field` object has `name` and `type `atributes, as well as attribute matching the names and meanings of the `field()` function's arguments.

To create a dataclass with a field that defaults to an empty list, try:
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+Line 71:
+== Functions ==



=== AsDict ===

{{{
import dataclass

@dataclass.dataclass
class Point:
     x: int
     y: int

p = Point(10, 20)
dataclass.asdict(p)  # {'x': 10, 'y': 20}
}}}

----



=== AsTuple ===

{{{
import dataclass

@dataclass.dataclass
class Point:
     x: int
     y: int

p = Point(10, 20)
dataclass.astuple(p)  # (10, 20)
}}}

----
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+Extract the `Field` objects from a dataclass.
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-=== KW_Only ===
+=== Make_DataClass ===
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+Line 127:
-A [[Python/TypeAnnotation|type annotation]] used for dataclasses.
+----



=== Replace ===

----



== Constants ==

'''`KW_ONLY`''' is a [[Python/TypeAnnotation|type annotation]] used for dataclasses.
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+Line 154:
-----



=== Make_DataClass ===

----



=== Missing ===

`dataclass.MISSING` is a sentinel value used internally.

----



=== Replace ===
+'''`MISSING`''' is a sentinel value used internally.
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+Line 163:

Diff for "Python/DataClasses"