Question 1

How to create a phantom type for email validation in Python?

Accepted Answer

Define a class inheriting from str and Phantom with a predicate using a regex or library like email-validator, then use parse() or isinstance() for validation. The library supports custom predicates for such use cases.

Question 2

Phantom-types or pydantic: which is better for type-safe parsing?

Accepted Answer

Use phantom-types when you need deep integration with static type checkers and custom runtime predicates. Pydantic is better for general data validation and serialization; they can be combined for enhanced safety, as shown in the pydantic integration example.

Question 3

Does phantom-types work with Django models?

Accepted Answer

Not directly; phantom-types lacks built-in integration with Django's ORM. You would need to manually apply phantom types to fields or use custom validators, which adds complexity compared to pydantic's seamless support.

Question 4

How to use phantom-types with FastAPI for API validation?

Accepted Answer

Since FastAPI relies on pydantic, define phantom types in your pydantic models as fields. FastAPI will automatically validate incoming data using pydantic's integration, as demonstrated in the documentation.

Question 5

What are the alternatives to phantom-types in Python?

Accepted Answer

Alternatives include pydantic for validation-focused use, typeguard for runtime type checking, or custom decorators with asserts. Phantom-types uniquely combines phantom types with both static and runtime validation, but may be overkill for simpler needs.

Question 6

How to handle parsing errors in phantom-types?

Accepted Answer

Use the parse() method which raises errors on invalid data, or integrate with try-except blocks. The library provides clear error messages for predicate failures, but custom error handling requires additional code.

phantom-types

What is phantom-types?

Overview

Use Cases

Best For

Related Projects

Found a gem we're missing?

Not Ideal For

Pros & Cons

Pros

Cons

Frequently Asked Questions