Create instances of dataclasses with the builder pattern.
Create instances of Python dataclasses with the builder pattern.
There are two ways to use dataclass-builder. Via a builder instance or by creating a dedicated builder.
Using a builder instance is the fastest way to get started with dataclass-builder.
from dataclasses import dataclass from dataclass_builder import DataclassBuilder, build, fields @dataclass class Point: x: float y: float w: float = 1.0
Now we can build a point.
>>> p1_builder = DataclassBuilder(Point) >>> p1_builder.x = 5.8 >>> p1_builder.y = 8.1 >>> p1_builder.w = 2.0 >>> p1 = build(p1_builder) Point(x=5.8, y=8.1, w=2.0)
Field values can also be provided in the constructor.
>>> p3_builder = DataclassBuilder(Point, w=100) >>> p3_builder.x = 5.8 >>> p3_builder.y = 8.1 >>> p3 = build(p3_builder) Point(x=5.8, y=8.1, w=100)
Fields with default values in the dataclass are optional in the builder.
>>> p4_builder = DataclassBuilder(Point) >>> p4_builder.x = 5.8 >>> p4_builder.y = 8.1 >>> p4 = build(p4_builder) Point(x=5.8, y=8.1, w=1.0)
Fields that don’t have default values in the dataclass are not optional.
>>> p5_builder = DataclassBuilder(Point) >>> p5_builder.y = 8.1 >>> p5 = build(p5_builder) MissingFieldError: field 'x' of dataclass 'Point' is not optional
Fields not defined in the dataclass cannot be set in the builder.
>>> p6_builder = DataclassBuilder(Point) >>> p6_builder.z = 3.0 UndefinedFieldError: dataclass 'Point' does not define field 'z'
No exception will be raised for fields beginning with an underscore.
Accessing a field of the builder before it is set results in an AttributeError.
>>> p8_builder = DataclassBuilder(Point) >>> p8.x AttributeError: 'DataclassBuilder' object has no attribute 'x'
A dedicated builder can make more sense if used often or when needing to document the builder.
from dataclasses from dataclass_builder import dataclass_builder, build @dataclass class Point: x: float y: float w: float = 1.0 PointBuilder = dataclass_builder(Point)
Now we can build a point.
>>> p_builder = PointBuilder() >>> p_builder.x = 5.8 >>> p_builder.y = 8.1 >>> p_builder.w = 2.0 >>> p = p_builder.build() Point(x=5.8, y=8.1, w=2.0)
The build function can be used instead of the method and must be used if the dataclass has a build field.
>>> p = p_builder.build() Point(x=5.8, y=8.1, w=2.0)
The following two statements are mostly equivalent, with the exception of documentation and type.
Therefore, see the section on Builder Instance for further documentation.
- Python 3.6 or greater
- dataclasses if using Python 3.6
dataclass-builder is on PyPI so the best way to install it is:
$ pip install dataclass-builder
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