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typing.get_type_hints Can Return Incorrect Type for Annotated Metadata #112618

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@cmg2146

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@cmg2146

Bug report

Bug description:

When running the following example:

from typing import Annotated, get_type_hints

class MessageCode(str):
    pass

class DisplayName(str):
    pass

class Message:
    field_a: Annotated[str, MessageCode("A")]

class Form:
    box_a: Annotated[str, DisplayName("A")]

hints = get_type_hints(Message, include_extras=True)
metadata = hints["field_a"].__metadata__[0]
print(f"MessageCode metadata type: {type(metadata)}")

hints = get_type_hints(Form, include_extras=True)
metadata = hints["box_a"].__metadata__[0]
print(f"DisplayName metadata type: {type(metadata)}")

the output will be:

MessageCode metadata type: <class '__main__.MessageCode'>
DisplayName metadata type: <class '__main__.MessageCode'>

when it should be:

MessageCode metadata type: <class '__main__.MessageCode'>
DisplayName metadata type: <class '__main__.DisplayName'>

This issue seems to occur only when:

  • the metadata subclasses an immutable type
  • when multiple instances of such metadata appear in different class definitions and they have the same value

CPython versions tested on:

3.9

Operating systems tested on:

Linux, Windows

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    3.11only security fixes3.12only security fixes3.13bugs and security fixesstdlibPython modules in the Lib dirtopic-typingtype-bugAn unexpected behavior, bug, or error

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