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Typing for metaclass examples · Issue #42 · fluentpython/example-code-2e · GitHub
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Typing for metaclass examples #42

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Typing for metaclass examples#42

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@jsrozner
jsrozner
opened on Apr 5, 2024

Consider the example in 24-class-metaprog/factories.py (corresponds to example 24-2, page 912 in my copy)

Dog = record_factory('Dog', 'name weight owner') 
rex = Dog('Rex', 30, 'Bob')

We do not get static type checking on, e.g., rex.name

Is there an easy fix, or is this because types in metaclasses / metaprogramming are hard?

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  1. ramalho commented on Apr 11, 2024

    @ramalho
    ramalho
    on Apr 11, 2024
    Member

    We do not get static type checking because all effects of metaprogramming happen at runtime, and a static type checker does not run your program. It can only analyze the static source code, and it is not smart enough to understand what record_factory does, or that the string `'name weight owner' is actually naming attributes of a class that will be built at runtime.

  2. ramalho commented on Apr 11, 2024

    @ramalho
    ramalho
    on Apr 11, 2024
    Member

    This is an interesting question, so I will leave the issue open until I work on chapter 24 for the third edition, hopefully in 2025.

    Thanks, @jsrozner !

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