commit a7c25bb01f2373eb1f113272731e1659bc91de95 · pyrox.dev/nixpkgs

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pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/utils.py
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       from typing import Any

     

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       _frozen_classes: dict[type, type] = {}

     

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       # make a derived class freezable (ie, disallow modifications).

     

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       # we do this by changing the class of an instance at runtime when freeze()

     

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       # is called, providing a derived class that is exactly the same except

     

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       # for a __setattr__ that raises an error when called. this beats having

     

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       # a field for frozenness and an unconditional __setattr__ that checks this

     

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       # field because it does not insert anything into the class dict.

     

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       class Freezeable:

     

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           def freeze(self) -> None:

     

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               cls = type(self)

     

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               if not (frozen := _frozen_classes.get(cls)):

     

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                   def __setattr__(instance: Any, n: str, v: Any) -> None:

     

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                       raise TypeError(f'{cls.__name__} is frozen')

     

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                   frozen = type(cls.__name__, (cls,), {

     

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                       '__setattr__': __setattr__,

     

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                   })

     

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                   _frozen_classes[cls] = frozen

     

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               self.__class__ = frozen