MyPy treats `Placeholder` as `_PlaceholderType`

Bug Report

Python 3.14 introduced functools.Placeholder so that you can create functions with partial() that choose which position arguments are filled in and which are passed through. However, MyPy rejects the typing of these values.

To Reproduce

From the docs

from functools import partial, Placeholder as _
remove = partial(str.replace, _, _, '')

Expected Behavior

MyPy recognises remove as partial function that takes two strings (the placeholders), accepts the placeholders as being placeholders for string variables, and the checks pass.

Actual Behavior

example.py:2: error: Argument 1 to "replace" of "str" has incompatible type "_PlaceholderType"; expected "str"  [arg-type]
example.py:2: error: Argument 2 to "replace" of "str" has incompatible type "_PlaceholderType"; expected "str"  [arg-type]
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.19.1
• Mypy command-line flags: mypy example.py
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.14

Inizia eseguendo con Python 3.14 la riproduzione mypy example.py riportata nell’issue e analizza come viene tipizzato functools.Placeholder e come viene gestito dall’analisi delle funzioni parziali. Il lavoro è completato quando l’esempio accetta entrambi i placeholder come posizioni di stringa senza gli errori arg-type segnalati.