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Dataclasses & What are they for
Dataclasses are an implementation of a code generator, similar to a Named Tuple.
The idea of using a code generator is to save time and reduce wordiness.
There are two views about the purpose of Dataclasses:
- It makes a mutable data holder, in the spirit of named tuples
- It writes boiler-plate code for you, simplifying the process of writing the class
These 2 world views are reflected in the name: “Dataclasses”
Per the dataclasses PEP, they are roughly a “Mutable named tuple with defaults”
They provide an elegant syntax for creating data holder objects
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A History Lesson
In the beginning there where:
- dicts for look-ups
- tuples for structures
- hand-written classes for more functionality
Later Named Tuples where added as a code generator with the goal of adding names to the fields of a tuple. This was limited by design, hence its name
ORMs appeared and pioneered using class attributes to specify rich data structures
In Python 3.6, it became possible to supply type annotations
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Comparison with Named Tuples
- Dataclasses are by default mutable
- Named Tuples have methods which start with an underscore which can be confusing. Ex: obj._replace(f=value)
- Named Tuples have legacy code. Ex: _asdict() returns an OrderedDict
- Named Tuples can be unpacked
- Dataclasses are faster at retrieving data but take up more space
- Dataclasses use functions instead of methods. Ex: asdict() vs nt._asdict()
- Dataclasses are underlying stored as instance dicts
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Generated Code Includes
- Dunder methods like init, repr, eq, lt, le, etc.
- Frozen nature by generating dunder methods for __setattr__ and __delattr__
- Class variables for the provided attributes
The code generation can be configured by providing keyword arguments to the @dataclass decorator
A complete list of methods and configurations can be found here
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A Complex Example of using Dataclasses
In the image example, the generated code includes:
- typed attributes
- hidden attributes from __repr__ response
- custom __hash__ dunder with the selected fields
- attribute with default factory value in __init__ constructor
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IDEAS CURATED BY
CURATOR'S NOTE
I started using Dataclasses and I think you should too
“
Pavel-Vlad Mateescu's ideas are part of this journey:
Learn more about computerscience with this collection
Understanding machine learning models
Improving data analysis and decision-making
How Google uses logic in machine learning
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