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Modelling Data with Dataclasses

Python

Write classes that hold data with dataclasses, and control their defaults, equality, hashing and memory use. Choose between a dataclass, NamedTuple and TypedDict, and turn outside data into typed records your code can trust.

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21 exercises

7 articles

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Your learning sequence

  1. 1 What a Dataclass Writes for You Read
  2. 2 Not solved yet. Sort Version Numbers with a Dataclass Practice · Easy
  3. 3 Not solved yet. Find Mutable Defaults That Instances Share Practice · Easy
  4. 4 Not solved yet. Hide Secret Fields When You Print a Record Practice · Medium
  5. 5 Not solved yet. Compute Cents from an Amount with __post_init__ Practice · Medium
  6. 6 Not solved yet. Fix a Dataclass Hierarchy with Keyword-Only Fields Practice · Medium
  7. 7 Not solved yet. Tell Fields Apart from Class Variables Practice · Easy
  8. 8 Why Some Objects Can Go in a Set Read
  9. 9 Not solved yet. Count Visited Cells with a Frozen Dataclass Practice · Easy
  10. 10 Not solved yet. Freeze Nested Data into a Hashable Cache Key Practice · Medium
  11. 11 Not solved yet. Predict Which Dataclasses Are Hashable Practice · Hard
  12. 12 Not solved yet. Sort Semantic Versions with Prerelease Labels Practice · Hard
  13. 13 Save Memory with slots=True Read
  14. 14 Not solved yet. Check a Class Before You Add slots=True Practice · Hard
  15. 15 Choose Between a Dataclass, NamedTuple and TypedDict Read
  16. 16 Not solved yet. Merge Overlapping Ranges with a NamedTuple Practice · Medium
  17. 17 Not solved yet. Update a Frozen Record with replace() Practice · Hard
  18. 18 Not solved yet. Convert Dataclasses to JSON-Ready Values Practice · Hard
  19. 19 Not solved yet. Parse Untrusted JSON into a Dataclass Practice · Hard
  20. 20 Not solved yet. Build a JSON Codec for Dataclasses Practice · Hard
  21. 21 Validate a Field on Every Assignment with a Descriptor Read
  22. 22 Not solved yet. Convert and Validate a Port Number on Assignment Practice · Medium
  23. 23 Not solved yet. Build a Generic Result Type with Ok and Err Practice · Hard
  24. 24 Not solved yet. Diff Two Dataclass Records Field by Field Practice · Hard
  25. 25 Not solved yet. Type-Check a Custom Dataclass Decorator with dataclass_transform Practice · Hard
  26. 26 Build Dataclasses at Runtime with make_dataclass Read
  27. 27 Not solved yet. Resolve Dataclass Field Types in Python 3.14 Practice · Hard
  28. 28 Dataclass Changes Across Python Versions Read

Check yourself

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0 / 5 correct

Why does Python reject Bad, while each Good object gets its own list?

Choose one answer to reveal the explanations. Answers are kept only while this page is open. 

from dataclasses import dataclass, field

try:
    @dataclass
    class Bad:
        xs: list[int] = []
except ValueError:
    print("Bad rejected")

@dataclass
class Good:
    xs: list[int] = field(default_factory=list)

a, b = Good(), Good()
a.xs.append(1)
print(a.xs, b.xs)
print(a.xs is b.xs)
Question 1 of 5