Type-hinting parameters with a sentinel value as the default

I currently use this strategy of a singleton object when I cannot assign default arguments in a function's signature and/or None already has meaning.

from typing import Optional

DEFAULT = object()

# `None` already has meaning.
def spam(ham: Optional[list[str]] = DEFAULT):
    if ham is DEFAULT:
        ham = ['prosciutto', 'jamon']
    if ham is None:
        print('Eggs?')
    else:
        print(str(len(ham)) + ' ham(s).')

However I get the following Error from mypy:

main.py:7: error: Incompatible default for argument "ham" (default has type "object", argument has type "Optional[List[str]]")
Found 1 error in 1 file (checked 1 source file)

• How do I type-hint ham without getting errors in mypy? or
• What strategy should I use instead of DEFAULT = object()?

Something I like to do — which is only a slight variation on @Blckknght's answer — is to use a metaclass to give my sentinel class a nicer repr and make it always-falsey.

sentinel.py

from typing import Literal 

class SentinelMeta(type):
    def __repr__(cls) -> str:
        return f'<{cls.__name__}>'

    def __bool__(cls) -> Literal[False]:
        return False


class Sentinel(metaclass=SentinelMeta): pass

main.py

from sentinel import Sentinel

class DEFAULT(Sentinel): pass

You use it in type hints exactly in the same way @Blckknght suggests:

def spam(ham: list[str]|None|type[DEFAULT] = DEFAULT): ...

But you have the added advantages that your sentinel value is always falsey and has a nicer repr:

>>> DEFAULT
<DEFAULT>
>>> bool(DEFAULT)
False