Correctly infer x: SomeEnum; x.name as union of literal names
#18797
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sobolevn
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Mar 13, 2025
Hi! I am working on mypy in python/mypy#18797 And I've noticed a small thing in your code. Ideally, `SomeEnum.Item.name` should be inferenced as `Literal[NAME_ONE, NAME_TWO, ...]` But, since you later modify `status` (which is the name of a enum item), it should be explicitly annotated as `str`, not `Literal`.
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I opened psycopg/psycopg#1023 to fix a "problem" is psycopg. |
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Diff from mypy_primer, showing the effect of this PR on open source code: psycopg (https://github.com/psycopg/psycopg)
+ psycopg/psycopg/pq/misc.py:158: error: Incompatible types in assignment (expression has type "str", variable has type "Literal['IDLE', 'ACTIVE', 'INTRANS', 'INERROR', 'UNKNOWN']") [assignment]
+ psycopg/psycopg/pq/misc.py:170: error: Incompatible types in assignment (expression has type "Literal['OK', 'BAD', 'STARTED', 'MADE', 'AWAITING_RESPONSE', 'AUTH_OK', 'SETENV', 'SSL_STARTUP', 'NEEDED', 'CHECK_WRITABLE', 'CONSUME', 'GSS_STARTUP', 'CHECK_TARGET', 'CHECK_STANDBY', 'ALLOCATED']", variable has type "Literal['IDLE', 'ACTIVE', 'INTRANS', 'INERROR', 'UNKNOWN']") [assignment]
+ psycopg/psycopg/pq/misc.py:170: note: Items in the first union not in the second: "Literal['OK']", "Literal['BAD']", "Literal['STARTED']", "Literal['MADE']", "Literal['AWAITING_RESPONSE']", "Literal['AUTH_OK']", "Literal['SETENV']", "Literal['SSL_STARTUP']", "Literal['NEEDED']", "Literal['CHECK_WRITABLE']", "Literal['CONSUME']", "Literal['GSS_STARTUP']", "Literal['CHECK_TARGET']", "Literal['CHECK_STANDBY']", "Literal['ALLOCATED']"
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Should this also handle unions of literals? I notice if you narrow with |
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@TeamSpen210 please, share your examples, I would be happy to support them as well :) |
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Closes #18786